The 5-foot-diameter hole drops 20 feet down, and the hole itself is a trap. If a Medium creature climbs down the hole, the sand collapses and buries the creature, threatening to suffocate it. Clearing out the loose sand requires 5 rounds of digging.
Characters can avoid this hazard with a successful DC 15 Strength (Athletics) check or by jumping down the hole and taking 7 (2d6) falling damage instead. A creature buried by the sand must succeed on a DC 15 Constitution saving throw or begin suffocating after a number of rounds equal to its Constitution modifier (minimum 1).