This is the quest location in Marleybone where you retrieve a key to open up Celestia. You get this quest after completing Dragonspyre. However, it no longer is necessary to get this key to go to Celestia. I like to do this for the experience rewards, and some nice loot drops. I'm not so sure this is a solo-able experience at the "appropriate level" of a character just finishing Dragonspyre. There's quite a number of levels to traverse to the top, and all the battles are with four opponents. There's a lot of life, balance, and frost enemies, so count on shields galore, and weaknesses on yourself. If you're able to bide your time with shields and cost-effective life gains, you could try and build up for a single large multi-hit spell. They will be shielding, and if you're death, often with combination shields that will really mess up your spells. You will need to do a hit that is generally at least 2500 damage (to overcome the shields). Even if you don't take them all out, you will be able to pick off at least 2, which will make the rest of the fight easier. The enemies will sometimes do vampire spells, but I don't remember seeing any life gaining (at least for non-boss encounters).
The tower levels
Here's the overview of the tower: http://wizard101.wikia.com/wiki/Warehouse_(Spiral_Geographic)
One: NPC, can be ignored
Two: four monsters
Three: four monsters
Four: puzzle encounter
Six: four monsters
Seven: four monsters
Eight: puzzle encounter
Nine: four monsters
Ten: boss encounter
Level Four Puzzle
If you read the book near the entrance, it will have a story with the clues on what to do (they will be the bolded words). Looking at what else is in the room, you have 5 crates in a horizontal line - one center crate, two to the left of it, and two to the right of it. You will click the crates in this order: center crate, the crate to the left of that, the next crate to the left of that, head back to the right and click the next crate, and the last crate to the right of that.
For those more visually oriented: 1, 2, 3, 4, 5 (order of crates from left to right)... click in this order: 3/2/1/4/5.
If you get the puzzle right, you get red health wisps. If not, I think a four monster fight. It's in your best interest to get it right!
Mini-boss General Stormclaw
He starts out alone, but after the first turn, he will cast a free earthquake and summon his 3 skeletal minions (lazy, tired, and dimwit). He will also cast a free tower shield on himself that gets replaced every time it goes away. While his minions are up (and occasionally after they are killed) he will automatically remove traps and weakness on himself and his minions (if they are up). There's a bunch of cheats and rules about targeting him while his minions are up, so it's best to either use multi-hit spells or just go after the minions first. In other words... just use big multi-hit spells in the same way you were doing with the regular four monster levels. You must kill the minions before you go after Stormclaw, or all sorts of extra spells will be fired on you. Plus, if you need to put a myth prism on him, you will need those minions gone for a chance to keep the prism trap on him.
When his last minion is dead, he will cast a free Frost Giant on you, so be prepared for a big hit and stun.
Level Eight Puzzle
This is impossible to solo and not trip the trap to fight four monsters. The floor is arranged with a maze of floor pressure plates: 3 of them are sun sigils and the rest are snake sigils. Hitting a snake sigil will fire off the trap and the four monsters will appear. Stepping on a sun sigil will activate it, but the character has to remain standing on it, or else it will go back dark. When all 3 suns are lit, a fourth character can pull the lever. If you do have four people, send the first character through the maze to the lever by the gate. Don't step on snakes! The second one goes to the third sun farthest along the maze. The third character goes to the middle sun, and the final character goes to the first sun. Then pull lever. Since I solo this, I never see what happens (I expect wisps to appear).
Boss Estrakir Gloomthorn
He's a robed insect minion of Morganthe. And this room is one of the more difficult cheat boss encounters in the game. Even a high level character may find this encounter to be quite difficult. In the accompanying dialogue, he drops a vital clue: you must at some point cast a global bubble spell of any kind. Otherwise, Estrakir will cast free Power Novas (that are fire based) every other turn. It might be a good idea to hold some bubble spells in the treasure card section of your deck so that you can get one out quickly.
Like General Stormclaw, Estrakir will automatically remove traps and weakness from him and his minions for free (at least while his minions are up). His rat minions will sometimes cast special tower shields that reduce damage by 90%. Multi-round damage spells could be a nice solution to that. He also has a minion named Knuckles who likes to cast free heals if your or your allies cast a heal. He will do a free Rebirth (but with no extra damage shield) out of turn when that happens. Drains and damage spells like Link and Vampire don't trigger this.
If you do target Estrakir while Knuckles is still alive, Knuckles will cast a free Helping Hands heal on Estrakir, and Estrakir will cast a free Fire Dragon.
You need to kill the rats first (since those shields they cast are too powerful), and then kill Knuckles. Multi-target spells are acceptable and won't trigger the above effects. Once the rats are down, you should probably heal up, unless Knuckles is low on health. Likely because of the shields, Estrakir will still have lots of health, so Knuckles healing him back up won't make much of a difference. Once all the minions are dead, Estrakir will start casting free Scarecrows on his turn (not sure if he does this if you have your bubble up or not... I'll amend this if I find that to not be the case). You may want to have some death shields prepared in your deck for this.
You'll need a lot to go right to defeat this encounter solo, unless are significantly high level. If you have a bubble aura up, and you take down the minions in the right order... you should have a solid shot though.