My hometown has the largest urban forest in the world. The forest is the largest forest completely surround and inside city limits. You have to drive around this forest to get anywhere. It is about 7 miles in diameter. The possibilities of a city completely surrounding a large forest are astounding. Secret tunnels, tribe of elves, centaurs, sprites, etc. Or you could go the evil route, goblins, kobolds, ogres, whatever. Our woods are FILLED with coyotes, deer and snakes, right in the middle of the city, so a lot of wildlife would be here, no telling what kind of flora and fauna would be in a fantasy world.