This country park in Hillingdon has some nice footpaths taking you to grassland and two pretty lakes. It is the largest public park to be built in the London area in the last 100 years, having been opened in 2000.
The site includes riverside paths along the Wraysbury River and the River Colne. There's also some moderate hill climbs with extensive views towards London and Windsor Castle.
The park is located near to Heathrow Airport so there's good views of the planes taking off. It's a good place to visit if you've got a bit of time to kill before heading to the airport.
There's parking available at the southern end of the park off Tramac Lane and Accommodation Lane. The park is also just a short walk from Harmondsworth village. Cycle Routes run from Windsor and Eton to the park as well.
Just to the west of the park you can pick up the Colne Valley Way and visit Wraysbury Reservoir and the lovely Staines Moor. This large area of grassland attracts grazing horses and cattle with a variety of birdlife around several streams and reservoirs. It's a great place to extend your walking in the area.