Each row/column must contain one different color building. Click on each square to change the buildings. The numbers on the edges indicate how many buildings you can see from that position.
Adapted from [url=http://www.recercaenaccio.cat/jocs-i-recursos-educatius/gratacels/]http://www.recercaenaccio.cat/jocs-i-recursos-educatius/gratacels/ [/url].