SNOLAB is the deepest clean-room physics laboratory in the world, 2,070 metres below the surface inside an active nickel mine. The shielding rock screens out cosmic radiation, which makes it possible to look for dark matter and other particles that would be drowned out anywhere closer to the surface.
You cannot just walk in — visits require advance booking through the lab's public programme, and only a handful are offered each year. For most travellers the real way to engage with SNOLAB is the dedicated gallery at Dynamic Earth, which explains the science and the engineering and includes a recreation of the underground lab.