A powerful force since medieval times, the thriving Swiss capital is an appealing city of museums and collections. Bernmobil is the capital's transit service. A BernCard is valid on trams and buses that serve the city. A free bike service is also an option for getting around. The Historical Museum and the Collection of the Bern Museum of Fine Arts house the art and architecture of millennia. The Einstein House and the Paul Klee Center showcase the work of two of Bern's famous former inhabitants.