Lisbon is full of parks and gardens, many of them completely undiscovered by visitors to the city. Any residential neighbourhood is likely to have at least one of its own: the kind of park where families gather for Sunday picnics and locals go jogging before work. As a tourist, it can be a unique experience to explore some of these spaces.
If you happen to find yourself in the neighbourhood of Ajuda (which sits just above Belem, roughly 10km outside the city center), you might like to check out Parque Recreativo dos Moinhos de Santana. The name makes sense when you make your way to the top of the park: there you'll find two old windmills ("moinho" in Portuguese means windmill), built on a hilltop where they could catch the wind and use it to turn grain into flour. Now the traditional blue and white painted structures still look out over the park and the city beyond, and even though they no longer function they're a remnant of a simpler time.
The park itself isn't the biggest, but it has a unique layout due to the hilly terrain. There are stretches of grass to lie on, a children's playground, a workout circuit, a concrete skate area, and — perhaps best of all — a little pond covered in lilypads that, come spring, overflows with tiny green frogs and turtles.
Occasionally events like free concerts are held in the park, which is a perfect time to see it.
Parque Recreativo dos Moinhos de Santana is open from 9am to 6pm in Autumn and Winter and 9am to 8pm in Spring and Summer. It's free to visit.