There's an extensive network of buses, which is particularly important for areas trams don't reach, such as the suburbs and Amsterdam North. Amsterdam is currently testing hydrogen (fuel cell) buses. When the trams stop, the night buses take over, with 12 routes servicing all parts of the greater Amsterdam area. You need a different 'strippenkart', available in vending machines at metro stations. A full fare 15-strip strippenkart is €6.80 (a one-zone journey is two strips) and a 45-strip version is €20.10. You can check timetables on www.gvb.nl. There are also regional Connexxion buses bringing commuters and visitors to the capital. If you have the time for leisurely gablespotting, hop on the 'Opstapper', a little bus that trundles all the way round the Prinsengracht from Centraal Station to the Stopera. Just stick out your arm, and it will stop (very Harry Potter), and then tell the driver when you want to get off.