The Old Abandoned Warehouse, next to The Basement.
The Old Abandoned Warehouse is located next to The Basement of the apartment you start by (first island) and is a fighting arena. You will need the key to get in, which you can get from fighting the Drunken Warehouse Bandit in Skye's Bar at night.
Clearing out the Old Abandoned Warehouse yields a packet of Coca, increased Strength, Charm and money.