Defiantly low-tech yet accurate to the second, Big Ben is having its 150th birthday Sunday, its Victorian chimes carrying the sound of Britain into the 21st century.

It's a birthday the world can share in. The peals of London's favorite clock are carried globally by BBC radio, and its 315-foot tower, roughly 16 stories, is the city's most famous landmark.

But getting inside and seeing Big Ben, the sonorous main bell that gives its name to the whole contraption, isn't easy. Security measures mean few are granted admission, and there's no elevator, so those who are escorted in must climb 334 winding limestone stairs.