Get enough help from your friends to complete your cellar; alternatively you could contract Jim (in the Haven Commons) to do it for Bush Bucks. Once completed, your cellar will be accessible from your backyard.

SQuests - DoaC
Stage 1:
Reach Level 60

Stage 2: Build your cellar using one of the two options

Stage 3: Talk to Jim to finish up

Reward: 400 XP

Questline: House Construction