The Castle or Pyramid of Kukulcan, Chichen Itza, Mexico
The Castle is easily the most impressive structure in Chichen Itza simply because of its size. It is over 78 feet high (24 meters) and has 91 stairs on each of the four sides. Back in 2003 when we visited Chichen Itza for the first time, we could actually climb up those stairs and stand on top of the pyramid. Now, the pyramid is off limits after an accident happened. Even though the view was definitely worth the climb, I did feel very uneasy on top with everyone running around excitedly in a very small space and without any railings or other protection.