So, Walthamstow Wetlands: go there. It’s free, it’s enormous, and it’s proof that wildlife will live anywhere—even if that "anywhere" is sandwiched between a sewage works and a noisy train line.
You’ll leave smelling faintly of fish and feeling like a better person. Or at least, you’ll have a story about that time a coot tried to mug you for your crisps. And honestly, that’s a win in my book.