The Colosseum is amazing for its complex and advanced architecture and building technique. Despite being used as a quarry for building materials at various points in history, it is still largely intact. Visitors can see the tiered seating, corridors and the underground rooms where the animals and gladiators awaited their fate. Take in a tour where you can explore these normally off-limits areas, like the network of underground passages, chambers and cells. Or head up to the upper tier, which was recently opened for the first time since the 1970s. This third level was where members of the lower Roman classes sat when cheering the gladiators, enjoying bird's-eye views of the action below. From this unique vantage point, travelers can walk around and enjoy the views. Put simply, the Colosseum set the model for all modern-day stadiums, the only difference being that today's teams survive their games.