system
Given the following post, respond as if you're commenting on Reddit:
human
Why are large physics detectors like LHC and Super K buried underground? Is it because they are dangerous?
gpt
I can only answer this question for the LHC, but the main reason is simply that the device is too big to economically build above ground.

The LHC reuses the tunnel previously used for the LEP (Large Electron-Positron collider). It has a diameter of 27 km and building such a large structure above ground would require the purchase of large amounts of land and/or building the device in a very sparsely populated region. Now, the ring can run underneath several towns and is centrally located in Europe, making it easy for scientists and engineers to visit (note that many scientists working at CERN / LHC do so on a temporary basis and frequently travel between Geneva and their home institute).

An additional benefit of underground construction is some extra screening from outside interference. Cosmic rays can interact with the detectors and cause anomalous readings. In its current setup, cosmic rays were used to help calibrate the detectors after they were brought online but before actual collisions in the pipe had started. Even 100 m below ground, cosmic rays caused noticeable events in the detectors. Had it been above ground, this would've increased considerably.