Why not add into the Advanced Training Hall, depths just like the ones in the Clockworks, that contain the same hazards/puzzles/challenges you see in the Clockworks, and depth-like area's that contain specific mosnters that you want to fight that are in the Clockworks.

A bit more detail into this post:
Think about it, what is a Training Hall for? Training. So why not add free-to-play depths/depth-like areas that cost nothing to do, but at the same time provide no profit in any way except training against the many monsters and preparing for the many puzzles/challenges in the Clockworks?

What I mean by training against monsters is that you will fight in the depth-like areas to build skills to deal with the various monsters of the Clockworks. I'm not talking about no short tutorial about what the monster does or what damage they deal (I know that it tells you what damage they deal/there resistances/what damage type is nuetral to them in the Help). But what I am talking about is a session that lasts as long as you like so you can analyze the movements of monsters, there weaknesses, and just build skills to deal with the monsters when you actually go into the Clockworks.
Sure, you can just do this in the Clockworks, BUT, there is only so many of one enemy in each depth, and you may need more experience against that particular monster that isn't there anymore if you killed of that kind of monster. AND, this way, there is no penalty for dieing in these depth-like areas, revving is free so you can keep training. In normal depths, when your first start out in the game, you really don't know how to deal with the enemies yet so you die more easily and the end result is that you waste more energy than you would want to unless you had training to deal with them. They could use these depth-like areas to train against the monsters (Yes i know I keep saying pretty much the same thing over again) so that they perform better when they actually go into the Clockworks, improving there overall survival rate in the clockworks, which pretty much means they'll die less and not need to spend energy on revving.

For example: You want to learn how to deal with Devilites and how you should proceed to fight them, just go into the Training Hall, go into the specific depth-like area with Devilites in them, and fight them until you can create an effective method for yourself for dealing with Devilites!

Or: You want to find ANY weaknesses you can of Greavers. So you go into the Training Hall and fight against them until you realize that there attacks can be interuppted.

What I mean about the training for depths is just that, training for depths.

They're just like normal depths ('cept for costing no energy and gaining no profit of any kind (Crowns, Materials, Heat)) but are only there for building insight against the many hazards and puzzles and challenges in the Clockworks.

Example: Let's say that you've never been in an Arena before, but go into a free-to-play depth of any kind (Remember, no profits) to train and find techniques for dealing in the enclosed box like room. And in doing so, you learn the many hazards that can happen in there (Like, getting trapped in the corner by a Trojan with no way to get out.)

Or: You want to train against Danger Rooms because there too hard for you now but you really want to complete them. So you go into a Clockwork Tunnel/Area that has a Danger Room traing depth, and you learn how to fight in Danger Rooms that have Status Traps, Spikes, or the Bramble 'wall' in the middle.

This would not only provide training against the monsters or against the depths of the Clockworks, but would also be a way to kill time when your energy has run out!

Any modifications to this, and any feedback about this idea is welcomed.

P.S.: I don't know if there is/was a thread like this before, so if there is, forgive me.