Maw Bank
Maw Bank is a common relic that grants 12 Gold every time you climb a floor (complete any room and move to the next). This applies to every floor including normal fights, elites, shops, events, and rest sites. The caveat is that the relic stops working once you spend Gold, specifically once you visit and purchase from a shop.
Maw Bank is a significant Gold generator early in a run. Climbing floors is unavoidable, so the income is automatic. If you save your money until the Act 1 shop and then spend there, Maw Bank's passive accumulation can give you substantial funds. The relic is best treated as a reason to delay spending: the longer you go before buying anything, the more Gold you stockpile. It becomes less useful once you have visited a shop, so timing your first purchase carefully to maximize the banked Gold is key to getting full value from it.