Indisputably one of the world's most historic cities, London attracts intrigued visitors from all around the globe every year.
Many are keen to enjoy the more modern tourist attractions, such as the London Eye or the impressive-looking O2 Arena, which hosts lots of top-class entertainment throughout the year.
And yet many of the capital's most historic landmarks, such as the Houses of Parliament and St Paul's Cathedral, have an enduring appeal.
It is worth noting, however, that there are still a number of sights that fly under the radar of most tourists.
And what's more, they won't cost you a penny.
Roman Londinium was founded 2,000 years ago and there are very few signs of that city left. But if you can dig below the surface, you can still find some fascinating traces.
Intrigued by the prospect? Well, start your hunt near the Tower of London, where you'll find a statue of emperor Trajan guarding the tallest section.
From there, head north (away from the Thames) into the plaza of the Grange City Hotel, which is home to the most impressive section of Roman wall.
And if you then turn to the Square Mile, you will move along London Wall where there is lots of evidence of the Roman influence.
For history buffs (and those keen to save a bit of money), it really is well worth taking a tour of Roman London.
But for a more conventional insight into London's history, you may wish to visit one of the city's great museums.
The Imperial War Museum, for instance, is a major tourist attraction, welcoming groups from all around the world.
Meanwhile, the Museum of London stages lots of entertaining exhibitions and events throughout the year, meaning your thirst for knowledge is sure to be satisfied.