For tourist it is not really recommendable to use a taxi. If you don’t speak Czech, most taxi drivers use a longer way and go through the whole city. So save money and take the underground/tram/bus! Also avoid taking any cab parked near the major train stations at all cost. Better to call up the cab company to prearrange a cab. Most drivers are nice but will rip you off unless an agreement is made – sometimes to 3 or 4 times what you should normally pay.