This spectacular brick-and-stone church (1903) is the headquarters of the Roman Catholic Church in Britain. Adorned in retro-Byzantine style, it's massive: 108m (354 ft.) long and 47m (154 ft.) wide. One hundred different marbles compose the richly decorated interior, and mosaics emblazon the chapels and the vaulting of the sanctuary. If you take the elevator to the top of the 82m (269-ft.) campanile, you'll be rewarded with sweeping views that take in Buckingham Palace, Westminster Abbey, and St. Paul's Cathedral. The cathedral's renowned choir usually performs daily: You can download the current timetable from the website.