Hoover Dam

The Hoover Dam, once know as the Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Arizona and Nevada. It is 700 hundred feet tall and was built in 1930. It was named after President Hoover and built during the Depression.

The Titan's Curse
After narrowly escaping the Junkyard of the Gods, Percy, Zoë, Grover, and Thalia traveled in canoes to the Hoover Dam with the help of some water nymphs. Seeing Bessie the Ophiotaurus, Percy tells it that it shouldn't follow him and it could be in danger. With everyone tired, they decide to go to the dam snack bar, and make some dam jokes that Zoë doesn't understand. When the skeletons arrive, Percy was forced to hide in an elevator heading into the dam, where he encounters Athena (dressed as a tour guide) and also meets Rachel Elizabeth Dare (a mortal who can see through the mist). Percy was surprised by her and swings his sword, but it just phases through her as she is mortal. She tells him to hide in the restroom as she leads the skeletons in the wrong direction. The group escapes using the two Angel Statues, who were sacred to Zeus. Thalia asked her father for help and the two statues woke up and they flew away.

Trivia

 * It was said to be one of Annabeth's favorite pieces of architecture (evident as Percy, Grover and Thalia spouted random facts that they subconsciously remembered, as Annabeth used to repeatedly go on about it).
 * The name is the subject of some jokes by the characters; the word "dam" is pronounced the same way as a vulgar word, damn (the dam snack bar, a dam t-shirt, etc.), and the characters, who are tired and emotionally strung after the death of Bianca di Angelo, use the word to cheer themselves up. Zoë Nightshade however, does not understand the joke.