Eiffel Tower

Probably the most recognizable structure in the world. Tickets can be bought online in advance but tend to sell out within seconds, so be sure to check on the timeframes when they release tickets online for sale. Otherwise, the only options for going up the tower are to queue in line the day of, or contract a tour which is usually 3 to 4 times the normal price of admission. However, it's an international icon and worth going up at least once. Beware of pickpockets around and near the tower though, they will often approach, or appear as, single tourists taking photos on their phones, but in reality they're casing you and your bag to see how close they can get before taking your bag.