Kokiri Forest (L4D2) - L4Dmaps.com
This will make you nostalgia so hard you'll forget there are zombies and start looking for important items, such as the Kokiri Sword (which is actually in a chest where it's supposed to be). The hearts heal you for 5 health, but the safehouse you start in has no health packs.
Honestly, it's just awesome. Hard to beat on your own if you try for the Kokiri sword because your team will stop to shoot zombies and get hit by the boulder which can either kill them outright or down them, and you can't heal them fast enough without getting hit by the boulder too.