Valve once planned to release an unnamed submarine game, and hasn't yet given up on the idea.
That's according to Gabe Newell, who said that the studio had the idea even before it started work on Prospero, the sci-fi project it was due to release before Half-Life but never did.
"Well a lot of the ideas for Prospero have sort of influenced our other games subsequently," Newell told the latest Steamcast, when asked if the company could ever return to Prospero.
"So, you know, whether or not we actually go back and do that specific game I don't know, it actually has a lot of appeal to us, we're all sort of fond of it.
"Nothing every really dies here, it's just a question how long until we get around to doing it. We just have so many opportunities to do so many different things. I mean I even get emailed from people saying 'What about Ricochet 2?', which is kind of astonishing.
"We actually have twenty six people whose first Valve game they every bought was Ricochet on Steam, so like I said nothing ever appears to ever really die, you just haven't gotten around to doing it yet. I'd put Propsero into the camp. And even further back than Propsero, the other game that Mike [Harrington] and I were talking about before we'd even had anybody other than us working on it was a submarine game.
"Mike was absolutely certain there was an opportunity to create fantastic underwater visuals and gameplay, so if people want to know the even furtherest back thing we have haven't gotten around to shipping yet it would have to be the unnamed submarine game."
One idea Valve definitely didn't give up on was a sequel to Portal, which is due for release on PC, PS3 and Xbox 360 in April. Newell has suggested that the game's development is already "pretty much put to bed".