Villa Borghese is one of the largest parks in Rome (approximately 150 acres), and the most easily accessible for most visitors. It is located just to the north of the historic center:  you can access it by going up the Pincio stairs at Piazza del Popolo, or by walking up the hill at the top of Piazza di Spagna (and there's also a cut through via the Spagna metro station).  Within the park is the famous art collection of Galleria Borghese, but that is not the only museum in the park. The park is also home to Villa Giulia, with its collection of Etruscan antiquities, Galleria Nazionale d'Arte Moderna, a zoo ( Bioparco), various academies, and other attractions. The park itself is a peaceful, leafy expanse with walking paths, fountains, statues, a water clock. and much more: it's a green oasis in the midst of a busy city, and well worth your time to explore a bit.  If you are a runner, this is a good place to go.  It is also an excellent park to take children to, as you can rent bikes, multi-person peddle-carts (with a surrey), or boats on the lake.