Downtown Houston, rich in brash new buildings and almost empty thoroughfares, lies inside the I-45 loop, spreading over on each side of the I-69, but it is also the location of a huge network of air-conditioned underground and aerial passages, designed so its inhabitants can get around in the stifling summer heat, and lively gardens and parks. Make sure you visit these downtown districts: Theater District, the hip Warehouse District and the Skyline District.