I love how much you are aware of the changing seasons out of the city; there are numerous beautiful forests around Hertfordshire to go for a run, a walk or have a picnic. One of the best destinations for a day out from London might be Northaw Great Wood. The main entrance is located on the Ridgeway, the B157 from Cuffley to Brookman's Park.
The walk along the South Bank from Westminster to Tower Bridge will take you past a plethora or interesting sights and cultural hotspots. There's always something interesting going on too.
Behind Markfield Beam Engine is the River Lee which travels from the Chiltern Hills all the way to the Thames via Tottenham Hale. There is a special light along this stretch of the river possibly due to there being about 10 massive reservoirs behind the levee on the other side of the river, offering an amazing sense of space. A great place to walk, cycle and feed the ducks, swans, geese and coots.
A small place to eat with great vegetarian/vegan food just off Camden High Street. This place does an amazing buffet at a great price, as well as serving reasonably priced tea and juices.