Prague has a cheap and efficient public transport system consisting of an integrated network of buses, trams, metro and a funicular on Petrin Hill. The historic centre is compact and pedestrian-only, but trams offer an inexpensive way of seeing the rest of the city, and there are plenty of metro stations in the centre. Tram lines criss-cross the centre and are the best way to get around, after the metro. Buses need rarely be used, as they tend to operate outside the centre and are more irregular. After midnight, trams and buses offer a limited service, usually every hour. Tickets are valid on all modes of public transport, but must be bought in advance and validated before each journey. It's best to book taxis over the phone and demand a receipt for the fare before setting out. A car is expensive and unnecessary since much of the city is pedestrianised. Also, parking is a major problem and vehicle crime is fairly common.