Escape Boom is an escape game in Liberec which also provides an English version of the tasks. You are basically being locked in a room and you have an exact time for solving the riddles which will help you to get out, which is quite a fun! The team can be comprised of 3 - 6 people.
The price is 1200CZK for a team but with an ESN card you can get a 100CZK discount from the ESN Liberec! Ask the ESNers how to do that.