This dungeon opens at irregular times for an hour each time. There is no official announcement of the schedule. On the day of the event, the dungeon will be announced in the daily sign-in news. To find out your time, see Event Time Lookup.
Unlike Metal Dragons, this dungeon is also a great source of money. Killing a King will give 10000 coins, 5000 coins for a High and 1000 coins for a regular Gold Dragon. Every clear will get you 20000+ coins. The price for selling the gold dragons is also very high. Gold Dragons sell for 3000 coins, High Gold Dragons for 30000 coins, and King Gold Dragon for 300000 coins.