Fort Gilkicker in Military Road, Gosport, was to be developed into 26 beach side apartments before its former developer pulled out of the project toward the end of 2018.
Now the building has been put up for sale through property services firm Jackson-Stops, based in Chichester, with a guide price of between £5m and £5.5m.
The fort is still owned by Andrew Temperton and agents say the bill to turn it into homes could reach £18m.
Andrew Richardson, of Jackson-Stops, said the cost of the project is 'not for men of straw’ but insisted agents had already seen a raft of interest.
‘People have to prove they have the experience for a development like this and have got to prove their finances,' he said.
'We have had lots of phone calls and internet enquiries that we are now in the process of vetting.
‘If this was a three-bed semi, we probably would have had 20 viewings by now – but this is a lot more complicated.'
Planning permission has already been granted to turn the fort’s sea-facing arched gun ports into ‘very luxurious' town houses.
Meanwhile the centre of the semi-circle site is currently earmarked for four barracks apartments, but Mr Richardson said a developer could change this.
Leader of Gosport Borough Council, Cllr Mark Hook, is optimistic a new investor can get the project back on track.
He said: ‘I’m aware that Fort Gilkicker is back on the market and should somebody be interested in buying it, we would welcome the chance to speak to them about it.
‘The planning permission is still in place so it can still be developed – but it is one of those schemes that is expensive to develop.
‘Restoration by use is the best way to bring these buildings back to the public; there are so many of these historic forts in the area that people just don’t get the chance to see.’
The agents’ particulars say: ‘Fort Gilkicker is a former naval gun battery constructed between 1863 and 1871 to contend with the growing threat of invasion. It featured 22 gun emplacements in granite-faced casements positioned to guard Portsmouth Harbour and Southampton Water. Today it is a Grade II* listed building and a scheduled ancient monument.
‘It occupies a dramatic and commanding beachfront position on the tip of Gilkicker Point with spectacular panoramic views over the Solent towards the Isle of Wight. To the rear is Gosport & Stokes Bay Golf Club through which the private access road passes.’
As interest in the site picks up, Mr Richardson urged members of the public to be sensible.
He said: ‘Do not approach the site under any circumstances without a staff member.’