Late-spring afternoons and early evenings in San Diego are often perfect for a bit of exercise after work or before an evening meal. The daylight period is now nearly as long as it gets, and cool air sweeping inland from the coast keeps things fairly cool -- at least through the month of June.
Close and convenient Mission Trails Regional Park offers a number of short hiking trails, including the two described below, that are good for mini-outings with a little exercise in mind. Be aware that access to both of these trails is restricted once the sun goes down, however.
The Climbers Loop Trail was built (and is steadily being improved) by the rock climbers who practice their sport on the granitic crags of Mission Gorge, about one-half mile north of the park's visitors' center. The no-nonsense climb from the edge of Father Junípero Serra Trail (the paved roadway/bike trail through the gorge) first takes you expeditiously to the base of some crags known as Middle Earth. From that vantage, a downward gaze toward "lower earth," the San Diego River floodplain, reveals how high you have climbed. The next segment of the trail contours, roughly speaking (and very rough in its sketchy condition), over to the main Climbing Wall, where at least a few and sometimes many climbers cling to the rocks like human flies. After a final descent on the Climber's Trail, you reach the pavement of Father Junípero Serra Trail; follow it for 0.2 mile to get back to your starting point. The distance for the whole loop is one mile, and the elevation gain is about 400 feet.
The second mini-outing is a visit to Kumeyaay Lake, which occupies some former gravel pits that have been transformed into a first-class botanical and wildlife habitat over the past ten years. Park in the large day-use lot for Kumeyaay Lake on the south side of Father Junípero Serra Trail, near where that road intersects Mission Gorge Road on the east (Santee) side. Walk through Kumeyaay Campground and over to the shore of the lake, where you can follow short pathways that go either right or left around the lake. By late afternoon crickets and bullfrogs deliver musical sound effects, and waterfowl gliding across the lake surface kick up kinetic ripples for your viewing pleasure. Along the trail to the left you'll discover a small exhibit of Kumeyaay Indian traditional life, including a replica of an 'ewaa, a hut made of native plant materials.