I know about shadowrealm, but what do you fight in shadowrealm?
I was fighting shadow warriors at level 53, with a double exp boost, and it still wasn't going fast.
I notice fighting in chaos altar is going the fastest so far.
Shadowrealm is the fastest right now for non-members. You fight Pure Shadowscythes and Shadow Guardians there. The monsters at Altar are pretty much the same as the ones from Factory, which don't give the same rewards like the Shadowrealm monsters do.
If you're a member, you can do 'Dys-Geni-c Chaorruption?' from Cleric Dawn in /cleric. It gives you around 20k with an exp boost.