Being a frequent visitor of Walnut street I have visited Mercurios several times as well. I first visited the venue when it was still serving only gellato. They have a large variety of flavors and you can also taste them before making your choice! They will also make a milkshake with the gelato if you want to. A great place to get an ice-cream!
During the last years they have also created a nice restaurant. Their wood oven made pizza is delicious. Only catch is that the seating is limited so there can be a bit of a wait on busy nights.