St. Paul's Cathedral

Besides Westminster Abbey, St. Paul's Cathedral is arguably the other must-see church in London. With its imposing dome, the third largest in the world, St. Paul's forms a predominant spot along London's skyline. It's also a survivor: Although an older incarnation burnt during the Great Fire of London, Sir Christopher Wren's dome (completed in 1710) survived numerous World War II bombings.

Though some reviewers are incensed about the pricey admission, most recent travelers agree that a peek inside is well worth the extra coin. To make the most of your visit, reviewers highly recommend climbing to the top of the dome to the Golden Gallery. You'll have to hike up 528 steps, but after catching your breath you'll enjoy far-reaching views of the River Thames, the Tate Modern, and Shakespeare's Globe Theatre. And once you've seen the top, head below ground to the Crypt, which now houses a restaurant and snack bar.

Similar to Westminster Abbey, you can bypass a fairly steep entry fee by attending the Evensong service. The service takes place Monday through Saturday at 5 p.m., and on Sundays at 3:15 p.m. Make sure to check the website for holiday hours. Sightseers can tour the Cathedral Monday through Saturday from 8:30 a.m. to 4 p.m. Adults cost £15 GBP (about $24), students and seniors pay £14 GBP (about $23), while children (ages 6 to 17) cost £6 GBP (approximately $10). The cost of admission grants visitors entry to the cathedral floor, crypt, and the three galleries in the dome. Find the cathedral off the St. Paul's Tube stop.