21671 Gateway Center Drive is a Class B office building in the heart of Diamond Bar's prestigious Gateway Center business district. Built in 2008 and recently refreshed, the two-story, ~26,000 SF property delivers a polished, professional environment with on-site property management, controlled-access entry, 24-hour secured access, and ample surface parking. Suites are leased on a Modified Gross basis: landlord covers water, trash, property taxes, property insurance, CAM, and landscaping. Each suite has its own dedicated electric meter, so tenants run their HVAC on their own schedule — a meaningful advantage over full-service buildings in the area that shut AC off at 6 PM during Diamond Bar's hot summer months. Tenants carry their own liability insurance and bring in their own high-speed internet, with Spectrum service available throughout the building. The address sits less than a mile from the SR-57 / SR-60 interchange and is minutes from I-10 and I-210, putting Los Angeles, Orange County, and San Bernardino County within easy reach. Ontario International Airport (ONT) is roughly 15 miles east, and tenants are within walking distance of bus service and a short drive from P.F. Chang's, Olive Garden, Chili's, In-N-Out Burger, Holiday Inn, and Ayres Suites. Located in the affluent Walnut Valley submarket — median household income ~$130,000, top-tier schools, and one of Southern California's lowest crime rates — Diamond Bar is a draw for established professionals, growing tech and medical practices, and regional headquarters.