Location from Ben 10 by Man of Action / Cartoon Network
The hidden Earth base of the Plumbers — an intergalactic law enforcement organization that Max spent his career with and that Ben is technically affiliated with by inheritance and circumstance.
The Plumbers exist because the universe has threats that individual planets can't handle alone. They're intergalactic law enforcement — recruiting from multiple species, operating across star systems, using technology that puts most planetary militaries to shame. On Earth, they're mostly invisible. Max was one of their best. His career ended before the series begins, officially. Unofficially, Max Tennyson hasn't stopped being a Plumber in the ways that matter. Ben's relationship with the Plumbers is complicated — he's solved problems they couldn't, made decisions above his clearance level, and is simultaneously their most valuable asset and their most unmanageable one. He eventually becomes a deputized Plumber agent. The formal designation doesn't change much about how he operates.
The main Plumber facility on Earth is built underground, accessed through hidden entrances that look like ordinary maintenance access points. Inside it's a functional law enforcement facility with alien technology — scanners, cells, communication arrays, briefing rooms. The aesthetic is utilitarian. Plumbers are not decorators.
Also known as: The Plumbers, Plumber HQ