Eric J.
Yelp
The famed Prague Astronomical Clock, located in the Old Town Square. Quite a sight to see, although it's best to come as early as possible to avoid the crowded, peak times. There are crowds, but it's not ever unmanageable, even at the most busy times. Then again, I'm coming from New York, so my definition of crowds might be a little less lax than most people, ha. Nonetheless, we really enjoyed our time observing the clock and walking around the Old Town Square.
Built in the 15th century, it's sort of crazy how long it's been able to stick around. On the hour, every hour, there's a short puppet show that is perhaps, a little underwhelming, but worth taking a peek if you happen to be in the area at the top of the hour. This only happens during certain hours, so you might not be able to see this "show" at night after midnight.
A must-visit while in Prague, although it might not be something you need to spend a lot of time at. It's definitely worth touring the Old Town Square, however, both during the day, and at night. The lighting is pretty great, so you can get some great pictures, and there are plenty of bars and restaurants nearby. Whether or not you feel "entertained" by the clock, it's worth a look, and just remember to appreciate the history that comes with it.