The Time Chamber is the testing location for blades created in Master Bladesmith. It provides trials to test blades' sharpness and strength.
Every five levels you receive a crank key for the time chamber door, allowing you to select from previous levels up to the last five level checkpoint you've completed. Reaching the level is enough to get the checkpoint, you do not have to complete it.
As you progress through the levels, new items will become available at the store and new ore types will be provided by the mining machine.