In the heart of London is located this beautiful park, which, just as Central Park in New York, is known by pretty much everyone. Even though it's cold now and winter is almost here, it's always nice to be able to wander around a nice park with a warm coat on (or not, I mean, if you'd rather go naked I'm not the one to judge...), and Hyde Park is quite big, so there's lots of corners for you to spend some time alone if you want.
Most people stay near the Marble Arch entrance of the park (as you can see in the image below), since it's close to the main touristic areas (Piccadilly, etc.), so if you want to be away from the crowd I'd recommend you walk a bit further into the park so you can sit in more isolated places.
Hyde Park is divided in two by the Serpentine Lake, and on the other side (if you're coming from Marble Arch) you'll find the little Serpentine Gallery, where they host modern art exhibitions (although I've been there twice and haven't found anything I liked, but then again, we all like different things so go see for yourselves). Close to the gallery are the Kensington Gardens, one of the royal parks of London.
All in all, this is a quite nice park that is really worth a visit, especially since it is right in the center of London. Another park that is not too far away from the center of the city is Regent's Park - I didn't take pictures of it when I went there but I also recommend it. And since I'm recommending stuff, you should listen to Selfish Whales, a great band from Bloomington, IN that plays songs as beautiful as this one.
