Česky Raj is the Czech for 'Bohemian Paradise'. It refers to the large region to the northeast of Prague, generally between the cities of Turnov and Jicin. Rolling hills, lakes tucked into narrow valleys, castles, and countless enormous sandstone towers are the name of the game here. While the towers dot the entire northeast corner of the country, it is here that they reach some of their highest concentrations and consequently where climbing is at its most popular.
The towers are soft, poorly protected sandstone and range up to 200' in height. To climb on them, you must have joined the national mountaineering association. You must also be familiar with the local ethics- chalk is prohibited on most of the towers since it can cause chemical damage to the rock, and metal protection is swapped for knotted ropes and slings on account of the rock's softness. A typical Czech rack consists of 5 or so differently sized monkey's fists or other knots, as well as a handful of slings for threading pockets, etc. Since most routes are poorly protected due to the pro restrictions and a general lack of fixed hardware, be a competent climber before attempting routes here.
The main climbing area is about 5km south of Turnov, where direct trains from Prague arrive every 1.5 hours or so. There are plenty of hiking maps in the region, detailing the major trails that take you out of town and up onto the ridge where the towers are. It is very difficult to get lost here.