A walk in the park
Few things provide tranquility for the soul like fresh air, open space and...ancient Roman ruins? Yep. It's definitely not a staple in every big city park, but leave it to Rome to chose a space as beautiful as Villa Borghese as their center for all things outdoors while being just outside the city walls.
Villa Borghese is as breathtaking as it is vast and the perfect place for a picnic, a stroll, or a run to burn off some pasta. I came here almost every day after work in the fall for a quick run before the sun started setting at 4:30pm. Though it was a bit more crowded, I would come here on Saturdays too with a good book or a journal for a few hours to find some quiet away from the crowded touristy center.
There are gorgeous ponds, fountains, ruins, piazzas, museums, small fields, trails, great photo ops, and benches everywhere. Not to mention its just a short walk up from the Spanish steps.