The historic core of Amsterdam extends with a pattern of concentric semicircles from the main train station (Amsterdam Centraal) to the southwest. Tourists arriving by train usually walk south along the Damrak and Rokin streets. Several operators offer boat tours along the canals lasting one hour and showing the highlights of the historic centre. The canals are lined by typical Dutch style houses, which are narrow and have a hook at the top, which is used to carry furniture into the house.