I could tell you that you will discover another side of Prague that is only visible at night.
I could tell you how what once was a shop, cafe or some other business steps to one side and reveals a secret set of stairs hidden behind an Ice Cream machine that leads deep under ground to one of the countless hidden bars and clubs beneath the streets of Prague.
But what you'll really want to know is that for the first hour you can consume as much free Czech beer, shots and Absinthe as you can stomach can hold. Then you move as a group onto several other bars, where you are greeted with another free shot, before finishing at the largest club in Prague where you get in free without needing to queue.
You will meet a bizarre and fantastically wonderful mix of people, we had two Kon Tiki travel groups and a Stag Party. The beer is great, the bars are good, the guides are very good. My only criticism was that the club at the end was so full of smoke that we didn't stay there for long but then we were quite drunk and ready to go home anyway so it's only a small criticism.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC