The first thing you notice when entering the park of Hampstead Heath is the silence. The city of London is so full of noise you get used to that when it leaves suddenly, it's a shock.
When you think of London's famous parks, something in the line of Hyde Park comes to mind: a not-that-big, crowded and controlled garden, where tourists and children come to have a small breath of fresh air. On the contrary, Hampstead Heath is a 790 acres' park of grassy hills, forests, and ponds, therefore, everything you would want for a countryside walk. Going from one extremity to the other can take up to an hour so you have plenty of space to get lost in this wild garden.
On every weekday, the park is mostly empty, with only solitary people forced to walk their dog. The most famous part of it is Parliament Hill, especially its view, where everyone meets but don't be afraid to get out of the groomed trails and embrace the emptiness of the place. The view is still very surprising, as you wouldn't expect to be so aloft as the climb is not so steep. If you venture in the little patches of forest, you can even have many encounters with wildlife, even if it is only noise in the bushes. Just be careful to know in which direction you're heading; a mobile GPS location is always useful.
Inside the park is Kenwood House and estate (entry to both is free) that you can visit to see your 18th century house fantasies come true. The original building dates from the early seventeenth century and was known as Caen Wood House. The property was then acquired by the Muray family, Earl of Mansfield in 1754, until 1914. Sometimes policemen on horseback cruise around, that reinforces this out of time feeling.
On the weekends, especially when the weather is cooler, families and youth meet here to enjoy a picnic or an outing. As it is also open by night, it is the perfect place for your summer evenings, cooling with friends and a little wine. For the most adventurous, the ponds are opened to swim, in any season and temperature. You can, therefore, mix your bowl of fresh air with a bath of fresh water, most appreciable with the warm weather coming back.