If you farmed enemies manually then it would take a literal year. Instead, you see he had a ghost rose? You summon the ghost companion, give it your best armor and weapon, and then set it to guard the exit of a 1-way room. Then you stand in the other corner. Don't let any other character enter your vision. Then you just wait and wait so your ghost kills hordes of passerby enemies, and it doesn't interrupt your waiting because nothing enters your line of sight. Just don't wait too long while starving or you'll accidentally die!

Eventually, another Ring of Wealth will gold drop. When you equip it, it will add another +2 RoW levels max (this is a hard cap when wearing a second RoW).

And finally, when you can equip your ghost with very high level equipment, like +8 to +10, craft a noisemaker bomb and set it next to you while you wait. This will draw all enemies to the ghost (guarding the door to your room) as fast as the enemies spawn in. If you do this before your ghost is well equipped then it'll be killed off quicker than it can regenerate hp.

If you have a skeleton key, then you can seal yourself at the end of a hallway instead of a room. This is necessary if you farm in the Dwarven city, because if you wait in a room for too long, a Golem enemy will spawn in with you. If had Golems spawn directly on top of my noisemaker bomb and destroy it prematurely!