Immense amounts of green on maps acknowledge Rome has an abundance of city parks. Whether large or small, these are excellent retreat places helping keep the "Eternal" in the city, allowing needed breaks to keep you going indefinitely.
COLLE OPPIO linked with PARCO DI TIANO is where I spent the most time based on proximity to where I stayed and the Colosseum. On my first approach from the east heading west along Viale Del Monte Oppio, anticipation rose with every step knowing the borders skirted the Colosseum...and there it was beyond the groves of trees with the sun sinking behind. I'll never forget those first glimpses...nor following times spent gazing amid playful children under watchful supervision of nannies. Scattered about are ruins of Baths from Trajan, Diocletion and Caracalla. Below ground are remains of Nero's Golden Palace reviewed seperately in this journal. Avoid northern section hobo camps inside the park walls.
Just right of Santa Sabina Basilica atop the Aventine Hill is PARCO SAVELLO with seasonal rose gardens, orange groves. The highlight is an observation area on the western edge with spectacular elevated views across the Tiber towards the Vatican and also over the city. There are not many other reasons to come to this residential area...which makes it perfect for escaping crowds. Exit at metro-stop Circo Massimo for uninterrupted homage in the valley of the former stadium before making the uphill climb. Bus #27 also passes thru here.
PINCIO HILL & GARDENS border VILLA BORGHESE seperated by Viale del Muro and the walls of the ancient city. Take the metro to Flaminio, come into Piazza del Popolo to get your bearings and then proceed east up the massively steep hill. Pincio and Borghese might easily be one of the least discovered outdoor "jackpots" of Rome. Impeccably tended landscape beauty is combined with a large assortment of statues, fountains and other small monuments. Showers cut my visit short, but were a welcomed attraction to the lush greens in Spring. Food vendors sold snack/drinks. Within Borghese is Rome's zoo as well as a Museum-Gallery and Villa Guilia with arts/architectural features.
One area to avoid - On Capitol Hill in search of the Tarpeian Rock area (which was corridored off) I came across a western side park-like area. Unless you appreciate used condoms, hypodermic needles and paraphernalia, I suggest turning back the way you came.