The boys got an awesome set of blocks from my parents for Christmas and the last few weeks they haven't gotten really into building with them. We've built a movie theater, a baseball stadium (of course), a train station, a car ramp and other things but their favorite is to build towers or castles as Logan demands they be called.
The object is to build the skinniest tallest tower you can and then stand next to it to see who it is taller than. So far the tallest one was right in line with me and stood for a few hours without being knocked over. My only recommendation is to watch your head and your toes. Wooden blocks are not forgiving when they fall!