This attractive holiday home estate in the Welsh coastal town of Haverfordwest in Pembrokeshire in the UK offers plenty of bang for your buck. The unique property is made up of three separate units and can be found on Dark Street, a fitting address that alludes to what lies out of sight...

The coastal compound includes the Castle Lake House, a stunning five-bedroom townhouse that dates back to 1275, and two one-bedroom holiday lets, The Retreat and Le Durkestrete. Helpfully, each unit has its own entrance, allowing any visiting guests to maintain their privacy.

There are five floors inside Castle Lake House, and each room has been beautifully restored. Blending modern décor with historic elements such as exposed timber beams, the property is filled with character. As well as offering idyllic views of Haverfordwest Castle, which was established in 1120, the estate also comes with an attractive garden and a rather unusual addition located beneath the ground...

That's right, this coastal gem has its very own secret tunnel. Like something plucked from an Agatha Christie novel, the passageway leads from the lowest floor of the mysterious historic main house to the two holiday lets. Yet the tunnel's purpose is unknown; it's thought that the corridor may have originally led to an old cellar, but whatever the reason for its creation, we think the addition definitely adds to the allure of this charming coastal crib.

Lynnewood Hall, a spectacular neo-classical revival masterpiece, is considered to be one of the greatest surviving Gilded Age mansions in all of America. The stately home was once one of the finest pieces of real estate in Pennsylvania, but due to its tumultuous history, the magnificent mansion soon fell into disrepair – but it still harbours its fair share of secrets...

The turn-of-the-century estate can be found in Philadelphia and was built between 1897 and 1900 for US tycoon and art collector, Peter Arrell Browne Widener. Notable American architect Horace Trumbauer designed the great house, which spans 70,000 square feet. Constructed from limestone, it was designed in a T-shape and at one time boasted a truly awe-inspiring interior. It's thought to have cost £5.8 million ($8m) to build and has 110 rooms, of which 55 are bedrooms.

Trumbauer hired two interior designers to kit out Lynnewood Hall, Jules Allard et Fils and William Baumgarten. Together, they filled the house with a myriad of precious items. In fact, The Philadelphia Inquirer once described the property's interior as "dripping with silk, velvet, and gilded mouldings, the rooms furnished with chairs from Louis XV's palace, Persian rugs, and Chinese pottery, the halls crammed with art by Raphael, Rembrandt, El Greco, Van Dyck, Donatello".

Yet there's more to Lynnewood Hall than first meets the eye. When Leland Kent of Abandoned Southeast toured the property, he stumbled upon a clandestine tunnel, located deep in the basement. Little is known about the secret feature and it's not clear what exactly it was used for, though it could have offered a route for staff to navigate the house out of sight. It's thought to lead to the estate's carriage house, positioned in the grounds.

This one-of-a-kind mega-mansion can be found in Lake Quivira, Kansas. Built in 1993, the colossal property boasts a 17,755-square-foot interior and a 15-acre garden. Inspired by the Legend of King Arthur, the property landed on the market for £8.3 million ($10.9m) but seems to have finally sold for a mere £1.9 million ($2.6m). It features seven bedrooms, seven bathrooms and a multitude of fantastical details worthy of a fairytale...

From the mansion's bespoke stained-glass windows to its handcrafted dragon doors and pulpit taken from a church in Salem, Massachusetts, this pad certainly has plenty of personality. There's a grand living room, a commercial-grade kitchen, a library, a billiards room, a home cinema and a wine cellar but that's not all...

Hidden amongst the grounds lies a swimming pool and a grotto, complete with a network of hidden scuba-diving tunnels that run beneath the mega-mansion. Accessed by a number of pop-up holes and caves, the tunnels are filled with sunken treasures, including faux fossils and exotic fish. 

Outside, you can see the end of the scuba diving tunnels, which lead to an extensive outdoor pool, complete with a 35-foot waterfall. Elsewhere, there's also miles of paved walking trails, as well as 15 acres of gardens, water features and elegant statues. What more could you possibly need?

Dubbed 'the safest home in America', this 36,000-square-foot mansion in the suburbs of Atlanta is as secure as they come. Inspired by the Acropolis of Athens, the eight-bedroom Greek Revival pile boasts everything from a home theatre and bowling alley to an infrared sauna and infinity pool.

Yet the mansion's most impressive USP is its security features. Ideal for a former president, mafia kingpin or wealthy individual on the Witness Protection Program, the ultra-safe compound has a secret 100-foot tunnel that's straight out of a James Bond movie.

The bunker even has its own command centre, not to mention remote-controlled ballistic walls and doors that can protect against a missile strike or zombie apocalypse. Once listed for £23.3 million ($17m), the home was sold by Concierge Auctions in December 2018 for the bargain sum of £1.8 million ($2.5m).

Alton Manor in New Jersey went on the market in 2015 with Pat McKenna Realtors, priced at £2.1 million ($2.9m). The five-bedroom, 11,500-square-foot French Colonial mansion rocks a number of wow-factor amenities, including a 42-seater party bar and a state-of-the-art soundproof movie theatre.

The spacious property also has a large outdoor pool, complete with a two-storey pool house, as well as a mini casino with slot machines and a cinema ticket booth, containing a decidedly creepy-looking mechanical usher. Minus the horror movie puppet, we think it'd make the perfect party house.

The former owner built the tunnel back in 1999 at the height of the Y2K or Millennium bug scare, that as we all know, luckily came to naught. Buried 22 feet under the house, the passageway comes with its own air circulation and surveillance system, meaning the owner could remain safe and secure for as long as required.

This Grade I-listed townhouse in Brighton was put on the market with Brand Vaughan for £3.7 million ($5.1m) in 2016. The imposing 19th-century property has five bedrooms and was used as a holiday home by members of the Thai royal family during the 1940s and 50s.

The property's most charming feature, however, is its secret tunnel, which is located in the gardens out front. The discreet tunnel connects the gardens to the Brighton seafront and has a pretty fascinating history.

Recently renovated by engineering firm Gyoury Self, the tunnel is said to have inspired the famous rabbit hole in Lewis Carroll's Alice in Wonderland. Not the first property to inspire a novelist, Carroll visited the gardens on several occasions before the much-loved literary classic was published.

Staying with the Alice in Wonderland theme, this French-style custom-built property in Minnesota sprawls over 9,000 square feet. The handiwork of Schrader & Companies, the luxurious £1.8 million ($2.5m) family home has all sorts of enviable features.

Be that as it may, the most fabulous feature is the home's Alice in Wonderland-themed tunnel and playroom. The magical eight-foot tunnel is decorated with a white rabbit mural by Luna Murals and gets progressively smaller as it leads into the child-sized playroom.

Every kid's dream space, the adorable playroom, designed by Anita Sullivan, has an Alice mural, along with a miniature dining set, plus a cute teapot basket that little ones can use to store their toys.

This spacious 4,524-square-foot home near Spokane's scenic Iller Creek Conservation Area has a wealth of standout amenities. In addition to its five bedrooms and four bathrooms, the property boasts a high-end kitchen, several reception rooms, an amazing man cave, and a whole lot more besides...

The unique two-part property was sold in 2016 by local firm, Century 21 Beutler & Associates Real Estate, to one very lucky buyer for £504,000 ($700k), a snip at the price given its numerous amenities. 

Situated in the breathtakingly beautiful hill town of Civita di Bagnoregio in central Italy, Domus Civitas is an enchanting 14th-century palazzo built into the hillside. Renovated in 2011 by renowned architect Patrizio Fradiani of Studio F, the three-bedroom property is simply divine.

Amazingly, the historic palazzo is connected to a number of subterranean caves and Etruscan tombs by a series of secret tunnels. One of the caves even features a heated pool and hot tub, making for a blissful space to relax and unwind.

The palazzo houses a kitchen cave area too, along with a wine cellar stocked with the best vintage labels, a capacious fireplace and a formal Italian garden.

Situated in a quiet suburb of Melbourne, Australia, this mansion is harbouring more than a few surprises. Previously on the market for a whopping £6.7 million ($9.3m), the ultra-private three-bedroom, three-bathroom home would be the perfect retreat for a VIP looking to keep a low profile. Towering walls and hedging provide optimum discretion, while the spectacular backyard comes kitted out with a dining terrace and a luxe swimming pool.

Spanning almost 8,000 square feet, the spectacular home offers plenty of space – and style – for your buck. The master bathroom is draped in marble and comes complete with his-and-hers sinks and a colossal walk-in shower, while no expense has been spared in the living room. Yet the property is also hiding an impressive secret that elevates it to new heights...

Hidden on the driveway at the front of the house, is a secret trapdoor disguised beneath the gravel. The sleek garage door rises up to reveal a tunnel that runs beneath the property. Perfect for celebrities or secret agents looking to come and go without blowing their cover, this subterranean feature is lined with thick reinforced concrete walls, making it impenetrable.

Head down the tunnel and you'll find yourself in an impressive six-car garage, complete with a state-of-the-art lighting system – the ultimate way to highlight all of your favourite toys. The underground garage also boasts a sealed wine cellar that's perfect for storing priceless bottles of wine. As far as secret rooms go, this spectacular property definitely has a license to thrill!

This intriguing three-storey wood, steel and reinforced concrete home overlooks Lake Hamama on Japan's Pacific coast. It was completed in 2016 by architecture firm Yukiharu Suzuki & Associates. 

The home's most jaw-dropping feature though is its secret concrete tunnel to nowhere, which protrudes from the basement and is a fantastic place for the homeowners to kick back and soak up the views.

On top of providing a space to take in the vistas, the tunnel has a practical, environmentally friendly purpose, allowing plenty of fresh air circulation and no doubt saving the owners a fortune on their air-conditioning bills. 

One of two pavilions designed by London architects Carmody Groarke in 2018 for a country house in East Sussex, this concrete guest suite is situated on the banks of an artificial lake.

The dinky guest suite pavilion, which is lined with fine oak panels, contains a cosy double bed, vintage-style bathtub and a compact kitchen, plus a dramatic floor-to-ceiling window that looks out onto the lake. This snug hideaway looks right up our street!

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