The Spiral Knights are an order of technolgical warriors. Why not a training arena, where players are able to choose sets of monsters to fight against with the weapons they choose? Naturally, the training arena, by virtue of its purpose, would drop no crafting items, nor heat, nor crowns. It would be a good place for players to burn their time while waiting for their mist to recharge and for them to train their shield bumping, animation cancelling, monster specific tactics.

In the training arena, players get 5 lives. They keep fighting on till they run out of lives, or get bored. Think Clockwork Arena levels, but without the treasure boxes at the end. At the end of each arena level, players either continue with the training, or go back to Haven to enter the actual Clockworks.

The training arena would have 3 modes: Solo Survival, Co-op Survival and Hazarding modes.

Survival mode would have Survival 2*, Survival 3*, Survival 4* and Survival 5*.
Using Survival 2* as an example, players can only use 2* -3* equipments in that mode. For Survival 3*, 3*-4*. Survival 4*, 4*-5* and Survival 5*, well, that's obvious. Once players run out of lives, they are ranked according to the number of stages they survived against.

In Co-op Survival, it is the same as above,except you play with 1-3 other people.

In Hazarding, players use their equipments, but they are unable to damage the spawned monsters with them. Instead, using their equips they have to trigger exploding blocks and use status effect vials to defeat monsters. I imagine it to be something like an Arena-style area with block respawn pads covering the floor. These pads will randomly spawn explosive blocks and breakable blocks in different configurations. Players will use the exploding blocks to destroy the monsters. Naturally, players still only get 5 lives and are ranked by the number of stages they survived.

EDIT: Hmm. Maybe instead of a derelict part of the clockworks we get to see the VR training room of the Skylark. OOO have the backstory as that in the wilderness the SKs found the VR training room. Bringing it back to Haven they hook it up to the clockworks, where it begins siphoning power from the core, allowing SKs to train in it with the different training scenarios, as shown above.

Possible rewards would be 400CE for the highest ranked player on the training scenarios.

Some possible backstory for the Survival mode:
The original Spiral Knights lived on a planet where technologically advanced tribal groups waged war for the lost technology on the planet's surface. The Spiral Knights eventually subjugated all the other tribes and absorbed them, but not without countless knights sacrificed to fend off the invading hordes to allow others to escape. Relive the legend of the falled Spiral Knights with the Survival mode, pitting you and teammates against the endless waves of the Clockwork's denizens. Make your way to the top and win glory!

Comments are appreciated. So is deconstructive criticism. Suggestions appreciated even more.