http://www.roblox.com/Item.aspx?ID=16381913
Go here for sound and meshes!
Tranquility valley is the most open building game on roblox, with a huge and unique variety, including a city.
The field is 8+ baseplates, and there are 4 other hidden places to build such as:
A city
A valley
Snowy Mountains
A dark cave
When building tools are selected there may be a slight graphics error, and it should go back once you de-select it. Have fun.