Sudbury Neutrino Lab (SNO Lab)
Search for Dark Matter Experiment
This small scale prototype experiment is surrounded by ultra pure heavy water (in containers in the white boxes) to redeuce stray radiation and thus false positives.
Looking for bubbles and sound in a special container of highly purified liquid (I think it was distilled water).
More details on the experiment in case you have the stomach for it. Keep in mind this was in 2012, things could have changed since then.
Search for Dark Matter - full scale