We chanced upon Piazza Vittorio Emanuele II after visiting Santa Maria Maggiore. It is located opposite of the Vittorio Emanuele Metro.
What caught our attention was the different nationalities of the people in the park...there were Chinese teenagers playing basketball, Bangladeshi playing cricket and other nationalities picnicking on the grass, enjoying the hot summer sun.
There is a ruin in the piazza that was not mentioned in most guides- Porta Magica, remains of the entrance to a villa owned by the marquis Massimo Palombara da Pietraforte, one of the most well known 17th century alchemists.
Besides, if you have young children, there's a playground and play area at the Giardini Piazza Vittorio, which is within the same area...and my 2 year-old enjoyed herself while we took respite from the sun, eating gelato whlie watching her play.