Free things to do in London

I've been blessed to have been to London 7 times now, but unfortunately that means I've done most all touristy things there are to do. This trip has been more focused on eating (unfortunately not FREE) as many cuisines as I can and seeing all the FREE things that I can (haven't seen).
London can be very expensive to visit, but if you just look around there are FREE things to do on every corner...he are some of the ones I did this trip:

* One New Change- There are shops to walk around in and many great restaurants. My favorite was Bread Street Kitchen (owned by Gordon Ramsey). We ate here 3 time and it was delicious. Ones New Change also offers a great view of St. Paul's Cathedral that I saw on Pinterest and had to get my own shot.

* Trafalgar Square, National Gallery and National Portrait Gallery- Trafalgar Square offers great views of Big Ben as well as the Nelson Column. The Galleries are filled with beautiful art, my favorite being the National Portrait Gallery(it has a lot of Tudor paintings/portraits).

*Camden Locks and Market- Camden Lock Market is situated by the Regent's Canal on a site formerly occupied by warehouses and other premises associated with the canal (Wiki)Just amazing abundance of street food and household goods, decorative, ethnically-influenced items, and second-hand items or 20th-century antiques, many of them hand-crafted, are among the wares (Wiki)The Street Food is great, the hard part is picking what to eat.

*Saatchi Gallery- Now I have to admit I was hesitant to go, just because I haven't much about it and I didn't know if it would be a waist of time. However it turned out to be one of my favorite places to visit. The gallery is about 15 rooms filled with contemporary/modern art. Its not as overwhelming as major galleries and the art is actually good! Absolutely do not miss.

*Old Roman London Wall- Now this "attraction" is not all in one spot, you are going to have to walk about 2miles and keep your eyes open. There are several websites that have a list to guide you to all the spots where you can see the wall and its well worth a walk, even in 30 degree weather. If you can't walk the whole entire wall, there is a large piece outside of the Museum of London and you can see.

*Greenwich- Greenwich has a lot to offer, here are some of the few :
Greenwich Park - 180 acres of green space in this Royal Park and the venue for the events at the London 2012 Olympics. The park is stunning in all seasons with great views across London.
Greenwich Market - Famous for eclectic stalls and delicious street foods, the market is a 'must-visit' when you come to Greenwich.
Cutty Sark - Restored and reopened after being ravaged by fire, the Cutty Sark has returned to Greenwich. She's now lifted so you can walk around below her. (NOTE:There is a cost to go on the ship, but I just walked around it and looked)
Queen's House- The beautiful Queen´s House is England´s first classical building dating back to 1683
Greenwich Foot Tunnel-This tunnel links Greenwich with Island Gardens on the north side of the Thames
Prime Meridian

 *Guildhall Gallery and Roman Amphitheater- This is a place that in seven visits, somehow I missed. Even this trip I wasn't sure if I should spend the time, but once again just like Saatchi Gallery is was so forth the visit. The Guildhall Galleries have a few rooms, which to me is great because you can really take everything in and not be overwhelmed. The best part in my opinion is the remains of the Roman Amphitheater in the basement of the Guildhall. Absolutely forth your time and its FREE!

I hope you  get to see some/all of these awesome places. What are some of your favorite FREE London Attractions?