You can get 3 Gates of Ordeal Tickets, and the tickets can also be purchased from the Market and by using Gold.
Entering the Gates of Ordeal:
You can enter the Gates of Ordeal if you have the ticket. 1 Gates of Ordeal Ticket is consumed each time you enter the dungeon, and it is reset every day at 00:00:00 UTC.
In the Story Dungeon, you can send all of your soldiers except for the injured and those waiting for March, but they don't actually deplete your soldier inventory.
There is a max limit of how many soldiers you can send for each stage in the Story Dungeon.
Your soldiers may get injured in a battle, and you can heal your injured soldiers immediately by using Gold.
You can find items based on certain rate of probability when you explore the dungeon.
If you meet bandits while exploring, you will engage into the battle and you may also get some reward if you defeat them.
You will battle a Boss bandit at the end of exploration. If you defeat the Boss, you will keep all the items you found in the dungeon.
If you are defeated by the bandits at any part of the exploration, the exploration will terminate and you will keep the items you found until now.