This is the starting place of your quest in Minute Quest. Here resides the king, who speaks to you and sends you on your quest.  After defeating certain bosses, new options will be unlocked which can be accesed at the castle. These are listed below.

Equip This allows you to put on new or old gear and try out different combinations of items.
Go Out This allows you to exit the castle at 0.1km and either start off your quest or if killed, exit and try again.
Treasure This allows you to venture to a secret location, consisting of four areas, which at the end contains a mini-boss which is a randomly selected Monster with boosted stats which drops a treasure chest containing random loot.
Tunnel This allows you to venture beneath the world and exit along at points with structures. Beware as monsters are still found here and are more likely to have brutal status (indicated by the skull icon next to their name).
Training This is allows to you go through an area with monsters generated from your pet list and gain experience points. You however do not gain any gold from this area.