5 Best Day Trips from Mexico City | Condé Nast Traveler
"The Great Pyramid of Cholula is the largest pyramid in the New World. When the Spanish arrived, they built a church and covered the pyramid. Parts of the pyramid have since been excavated, notably, these tunnels discovered in 1931. The tunnels offer a fascinating look into how the pyramids were built and made bigger every 52 years. You can explore the tunnels, which span five miles, alone but if you want to know more about what you're seeing, you can hire a guide." - Susannah Rigg
