answering such questions is always full of fun. Well listing you down the names of modern video games which are the best for game marathons
1. World Of Warcraft
this game literally never ends, there is always something to do, and you can get so involved with wanting to develop your character with achievements that are either obscure or so daunting to achieve that they consume your time. Working to gain flight in the 6th Expansion pack Legion, has consumed probably over 100 hours of /played time for me.
It was definitely a grind, but enjoyable because of the story and lore. The great thing about this game is you could play it for hours and hours in PvE( Player vs Everything) or PvP (Player vs. Player) or you could do instances for hours on end trying to defeat the hardest boss with achievements that are not easily gained playing with a (group) guild of members. You can also solo quest if you like the storyline.