Windmill

The Wind Mill (or Windmill) is a Common Decoration that can be bought from level 32 on at a cost of 20. There are no to collect. However it does show the sign every 6 hours when 25K XP arrive.

Users of Tiny Village Wikia mentioned the following on the question what is the best buy referring to the Windmill (in May 2012) under the page Decorations:

Hey guys is it better to buy many stores to gain exp or spend cyrstals on windmills? BTW i have the 25th expansion and plan to build all stores and houses or all windmills. AND is the 20 crystals for the windmills the confirmed price? if soo time to exploit that lol once i reach level 32.

5 days ago by ID: TwiinZero

In my mind, windmills are much better. You don't have to worry about resources and you get 75,000 to 100,000 XP per day per windmill (depending if you can get 3 or 4 cycles in - they go in 6 hour cycles).

Also, they only take up 3x3 as opposed to stores which are usually 4x4 (some are smaller, some larger - see the stores page)

Yes, they cost 20 crystals.

5 days ago by Oioiaussie

lol of course windmills are better when we haAD THAT crystal glich yesterdaY on andorid i had 3400 crystals i spent it all on windmills. When update came i still had my windmills and an extr 100 crystals for compensation. I was level 33 yesterday im now lvl 35.

2 days ago by A Wikia contributor