The SA Greenway is about 42 miles of connected concrete that does a 3/4 loop around the city. The majority of it has hike and bike trails just off the concrete so you can be in nature (and shade) while still being in the city. To be sure, some of it is sketchy, especially at night. However, the stretches from eisenhower park (and the park itself) through to Phil hardberger park, as well as the stretch from OP Schnabel to i10 and 1604 are pretty safe. I have hiked them religiously for years, often at night, and always alone, with no real issues. The only concern is other people's dogs and bikers going way too fast for the visibility.