I have walked past the Somerset House millions of times without knowing it was even there. I saw on the Londonist.com website that it had free tours on Tuesdays and I love free!
Somerset House started off as a house for the Duke of Somerset (hence the name) who was Edward Seymour while Henry VIII's son, Edward, was king but too young to rule. This was an important place because it was between the Tower of London and Westminster.
Somerset House became the place where the queens stayed to include Anne of Denmark (James I),
Henrietta Maria (Charles I) and Catherine of Braganza (Charles II). The Old Palaces Tour gives great detail of the history of the place.
A lot of this place is free except for some of the exhibitions. They have other free tours on other days, which is another good way to see the whole house.
This is a very unknown treasure.
The Piazza and Central Market
Indigo Jones (the same person who painted the Banqueting House ceiling) designed this space. He intended it to be a residential square.
The buildings you see are actually Victorian.
It is always worth walking through if you are in the area. There is usually some street entertainment.
There are many shops here but usually high end, still lovely place to browse.