Wonders represent impressive architecture or renowned achievements that are recognized throughout the world. Unlike improvements or units, each Wonder can only be built once, and by only one Civilization. Wonders also have very powerful and unique bonuses creating a great strategic benefit in accumulating them. Wonders cost <l:6,93>production<e> and each requires a specific <l:6,66>Advance<e>. Wonders are usually obsoleted by world-wide Advances.