The trails at Philly:
Treetop Trail - this is the main one, and biggest. It creates a loop from one end of the rare mammal center to the other, going out and around the big eating area and fountain. It includes sizeable areas of trees for the animals to climb. It then goes south along the pathway, past the reptile house and along the children's zoo, over to PECO primate reserve and around the orangutan area. It is used by a host of animals - tamarins, fossa, lemurs, saki, mangabey, and others.
Big Cats - primarily tigers and lions, but also cougar, jaguar, snow leopard, and leopard. It goes over the main walkway in front of the Tiger Terrace eatery, down along the glass wall of the indoor eating area, and then under the gorilla trail.
Gorillas - Gorillas. Goes out from the eastern PECO entrance, across the walkway and west along the pond before making a loop. In the winter this trail is occasionally used by the big cats, as well.
Great Apes - Orangutans and gibbons. Similar to the gorilla trail, but it goes out from the orang yard near the western PECO entrance.
Meerkats - this one goes out from their formerly indoor-only enclosure and includes a winding trail next to the small mammal house. There's climbing tours, a big sand pit for digging, a statue that's half in and half out of the trail, and several other different ways for the animals to explore.
Red Pandas - their trail is primarily overhead, with lots of hidden spots for the pandas to nap. It can also be used by the lynx.
Otters - this one isn't much of a trail. One part is a little babbling waterfall type thing that then goes under a bridge to connect the two otter areas (their former exhibit and the area that used to be for the pelicans across from it), and another that goes up and over and ends with a slide.
Goats - I'm not sure if this is considered a trail? But it's part natural, part metal, and gives them a climbing area, then up to bridges and walkways, then back down to the ground and up to more bridges. There's several gates to allow keepers to separate animals and there's a climbing area for children that mimics part of it. The treetrop trail goes right along part of it.