And the redundant covered reservoir in a field near Bradford could be worth more than £1m when it's done up.
Several people showed an interest in buying the 11ft deep concrete bunker after it was put up for sale in March by owners Keyland Developments, part of Kelda, owner of Yorkshire Water.
The bunker's new owner is said to be a middle-aged professional from West Yorkshire and a man with an eye for the unusual.
The property off Beckfoot Lane at Harden, near Bingley, comes complete with planning permission and architect's drawings showing how the 90ft by 50ft underground water tank can be converted into a 3,800sq ft living space.
There is space over two storeys for five bedrooms, a triple garage, courtyard and covered winter garden. The curved roof is to be covered in grass to blend with the countryside.
No cost figure has been put on the conversion, but the end result will be a £1m-plus property.
Estate agent Andrew Hodgson of Dacre, Son and Hartley said: "It is a spectacular setting within the green belt and, although partly subterranean and surrounded by trees, there are exceptional views of Harden valley."
He described the property as "unique" and said it was one of the most unusual he had ever come across.
"There may be other redundant pumping stations and reservoirs that may have development potential on the back of this one. We have sold chapels and churches for conversion in the past but nothing like this. It has a cracking view and the concept of the house is eco-friendly," he said.
Mr Hodgson said Bradford Council planners had granted permission and were pleased with the design.
"It is a concrete bunker with a tin roof and it could eventually end up an eyesore if nothing is done with it," he added.
The estate agents' own blurb says: "Unique opportunity to create a spectacular contemporary dwelling to an eco-friendly design within the shell of a former covered reservoir in a beautiful rural setting in three acres of land... could this be your million-pound dream home?"
Ramsden Barrett Architects of Leeds came up with imaginative plans for a "spectacular contemporary dwelling" which planners have already passed.
The "green" ethos is satisfied by the living space being underground, which helps with insulation and should conserve heat.
But the owner could, if he wished, use rainwater collected on the roof to flush toilets.
Architect Paul Smith said it had been fun to work on a building which was never designed to be lived in, and added: "We think it's the ultimate James Bond headquarters."
A spokesman for Bradford Council said the designs represented an intelligent use of a site within the green belt.
andrew.robinson@ypn.co.uk