A trip on The London Eye is a must for all visitors to London and a great place to take photos. At 135 metres it is the world's tallest observation wheel and the perfect way to see the whole city. You can book tickets in advance from the official website. One whole rotation of the Eye takes 30 minutes and visitors step on and off without the wheel ever stopping. From the top, on a clear day you can see as far as Windsor Castle, almost 25 miles away.