Saguaro National Park surrounds Tucson on two sides — the Tucson Mountain District (West) and the Rincon Mountain District (East) — and protects the densest stands of giant saguaro cactus anywhere. The two halves are about 30 miles apart and feel different: the western unit is denser cactus forest and shorter trails close to the city; the eastern is wilder, with high-country trails up into the Rincons.
For a first visit, do the Bajada Loop in the West (an unpaved scenic drive with quick walks) and stop at Signal Hill to see the petroglyphs etched into the volcanic boulders. The Cactus Forest Drive in the East is paved and good at sunset. The annual saguaro flowering peaks in late May. Each district has its own visitor centre and small entry fee.