Always lock doors. Always.
Not doing so is risky to your safety, and the Town as a whole! To unlock/lock doors, fence gates, trapdoors, etc, simply shift and right click on the door.
Extra levels? Enchant books!
Towns are always in need of more enchantment books! Use the Arcanium in Town to enchant books without consuming any lapis. Note that this only applies when you have 30+ levels, as the Arcanium always uses maximum enchanting power.