As the others still mentioned Munich is worth a visit, but 6 hours are pretty short. I hope with 6 hours you meant you have 6 hours till you need to be at the airport again. You'll need abou 1,5 h to get from and to the airport and if you don't arrive on time, need to pass security and arrive 30 min before dep. for boarding all within 6 h, than you'll have less than 3 hours to visit the town. Can be quite a hassle. Anyway it can be still interesting even in such a short time.

Enjoy your trip.
totti