What is the [LONGEST] videogame you have played? Singleplayer only

For me it has to be Monster Hunter FU, albeit most of the content was intended to be done in multiplayer...

>>712453157 (OP)
Baldur's Gate 3 is long, so I'll say that.

The Hundred Line, easily.
It's difficult to convey the scale of the game. Basically the content of a trilogy packed into one game.