Valve, the developers of series like Half-Life and Team Fortress, were once working on something a little less fantastical: a submarine game.
Speaking on Steamcast, boss Gabe Newell says that he and company co-founder Mike Harrington had, in the very first days of Valve's existence, toyed with the idea of making a submarine title.
"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."
Before you say "lulz submarines", remember, this was the 1990s, when underwater games like Silent Hunter and Seawolf were big business.
And just because it was a submarine game doesn't mean it was going to be some boring simulation, either; one of my favourite games of all time is set underwater, and it was as much a sim as I am the King of Spain.