When I was playing dying light with friend we discovered that every timw you go to sleep and wake up air drop will appear, if you don’t know air drops are pretty rare and if you collext them and deliver to one guy you will recieve lots of xp, we used that multiple times to unlock grapling hook very early. Air drops also gave lots of medicine which was hard to get in early game and that very helped us
Quite possibly also in Dying Light. Me and a friend did the shop area, where you had to pick up supplies and turn off the electrified water, a ton on normal mode, but then turned the game to insane mode when we actually got back to the Tower and before handing them to the supplies guy, and got a ton of experience that way, since I’m pretty sure you got more exp in insane mode