Right before you get up to Othias, in Othias' Tower in the "city" Rain, there are some imps. You can kill the imps evry time you pass by, and every time you kill them, you get at least 10 gold peaces. You can go up to Othias, an down again, and again, and again and...
Ring of rocks
Before entering Othias's castle in the City of Rain, you will encounter little creatures with at least one or two bags of gold. You can go back and fourth every so often to load up on gold after destroying them.