SAN FRANCISCO, Calif. -

With attractions like the expansive Golden Gate Bridge, the eerie and historic Alcatraz, the bustling Fisherman's Wharf and the sweet smells of Chinatown, it's no wonder San Francisco played host to more than 16 million visitors last year.

But those visitors spent a pretty penny.

TripAdvisor announced its annual TripIndex Cities cost comparison study, revealing San Francisco as the most expensive U.S. city for 2014 summer travel, while Las Vegas holds its claim as the most affordable U.S. spot for the fourth consecutive year of the report.

TripIndex Cities study compares the cost of an evening out and overnight stay in 67 tourist cities around the world, taking into account typical costs for two for cocktails, a two-course dinner paired with a bottle of wine, round-trip taxi transportation, and a one night stay in a hotel during the summer travel months from June to August.

San Francisco emerged as the most expensive city in the U.S. coming in with a daily TripIndex cost of $508, followed by New York City at $501 and Boston at $491.

According to San Francisco Travel, hundreds of thousands of visitors a day on average in the city are spending a total of $25.7 million.

London shot up six spots from last year to be crowned the costliest destination on the international list.