20. Alamo Mission | San Antonio, TX
Most Americans are familiar with the phrase ‘Remember the Alamo,’ even if they’re not entirely sure about the events that occurred at this 18th-century Spanish mission. Later repurposed as a fortress, the Alamo witnessed a pivotal and bloody battle in 1836 during the Texas Revolution, which Mexico ultimately won. Today, it stands as one of the most frequently visited historical sites in the country, drawing in approximately three million visitors annually.