Well if you count racing games then it's no contest Nurburgring Nordschleife all the way.
For FPS
Duke Nukem launch facility
Half-life Datacore
Half-life Frenzy
Half-Life Stalkyard
Half-Life Subtransit
Unreal multiplayer map set on a space ship
Unreal DM_Deck16
Also countless of user maps for Half life and Unreal tournament I can't remeber the names of anymore.
Most played was the map a co-worker and friend made for half life of the office building we worked in at the time. 5 or 6 of us used to play that at the office at the end of most work days. Online has never been able to capture that kind of fun.







