courage-testing event; test of courage
An event, often held at night in a scary place, where participants test their bravery. Similar to 肝試し (きもだめし), but 試胆会 may imply a more organized gathering.
See also: 肝試し
A courage-testing event was held at the school during summer vacation.
At the test of courage, we ended up walking through the graveyard at night.