As a cottage with its own underground cave goes on the market, BBC News takes a tour of some of the other unusual homes that have challenged the descriptive abilities of estate agents.

Industrial behemoths, whimsical follies and surreal structures are among the properties that have gone up for sale in recent years.

The house on a rock

Image copyright Adam Gibbard

Perched on a craggy outcrop above Towan Beach in Newquay, this property was sold by Lord and Lady Long for £1m in 2012.

The island, which is known as both Towan Island and Jago Island, is reached by a private suspension footbridge. The titled couple, in their 80s, said they sold up because they wanted somewhere with a more accessible front door.

According to Visit Newquay, the house's occupants have included a reclusive Irish-Canadian eccentric who played the organ at night, and Alexander Lodge, who invented sparkplugs.

The current owners of the house, who do not want to be identified, lease the property out for holiday rentals - it costs £4,500 for a week in the summer.

No 1, The Thames

With imposing views and an equally imposing address, No 1, The Thames sold last year for a mere £500,000 - which may seem like a bargain for a seven-bedroom mansion within commuting distance of central London.

Situated a kilometre (0.6 miles) off the Isle of Grain, roughly where the rivers Thames and Medway meet, Grain Tower Battery is a bomb-proof fort built in about 1855.

The drawback? The 160 year-old estuary gun emplacement can only be reached by boat or when the tide is out.

The water-softening factory

Image copyright Savills

The Lime Works in Faversham, Kent, is currently on the market for £1.5m, a mere snip compared to its original sale price of £3.75m.

Described by estate agents Savills as an "impressive and highly individual conversion of two water towers into a spacious and contemporary home", the 1930s building was a functioning water-softening plant until 1942.

The new owner will be able to enjoy a heated rooftop swimming pool, cinema, motion sensor lighting and "hand-crafted concrete beds and baths".

Work on the house is only 90% finished, "which will allow the buyer to design and specify the final 10%".

Maybe some taps for the concrete bath would be on the list.

Image copyright Savills Image caption Hand-crafted concrete baths are included - but where are the taps?

The railway carriage

This house, named Tracks End, started life as a third-class Midland Railway carriage.

Decommissioned from the Tewkesbury Line in 1926, it was transported to Castlemorton, Worcestershire and turned into a two-bedroom house which went on the market in 2014 for £290,000.

A bungalow in Helston, Cornwall, was actually built around a railway carriage. Outwardly an ordinary home, Waverley's bathroom and two bedrooms are within the car, while the kitchen, hall and living room are in the surrounding structure.

Image copyright Care and co Image caption The Waverley bungalow has views over the Cornish countryside

Martello tower #55

Martello towers are small defensive forts - usually coastal - built during the 19th Century. They played a key role in defending the UK against the threat of Napoleonic invasion

Tower number 55, in Norman's Bay near Pevensey in East Sussex, sold for £285,000 in 2004.

Planning permission was granted by the local council for the tower to be converted into a two-bedroom house.

The water tower

Image copyright PA

The water tower in Burton Green near Kenilworth, Warwickshire, is a German-designed Art Deco building with protruding buttresses.

The Corporation of Coventry owned the tower before Severn Trent became responsible for water supply in the region.

It sold for £250,000 in 2013, with planning permission to convert it into a four-bedroom home.

The cricket pavilion

Image copyright Bedfords

This cricket pavilion in Thurston, Bury St Edmunds, sold for £215,000 in 2012.

The modest single-storey building was the pavilion in a neighbouring village and was moved to its current location in about 1930.

Take a tour of the cottage with a cave (in case you missed it).