The Belfast Welcome Centre, at 8-9 Donegall Square North (the street leading north away from City Hall) call book them for you. Telephone 028 9024 6609 or just call in.

In my limited experience, your tour depends greatly on the driver. I've had one fabulous tour and one with a driver who was much less interested or attentive. If you know of anyone who can recommend a particular driver, you can always contact them directly.

Your hotel might arrange one, but I'd recommend going via the Welcome Centre.