I am a lvl 55 Destroyer, with a boxed SE. I have read that there are 6 levels to GoE, and from what I can read, there seem to be mobs down there all the way up to around lvl 60. I tried going to the lower levels, and got down to around lvl 4 or so. I didn't keep a close count of the levels, but there were Garden Guardians, surrounded by several smaller monsters. I saw some doors for ramps going down to a deeper level, and stood in front of them for maybe 20 - 30 minutes. The doors never opened. Some other players came along, and 2 of them could walk through the closed doors, but I could not. How the heck can I get to lower lvls? The Cats and Necros are pretty crowded, so I'd like to see if this is an alternate place to grind for a few lvls with a polearm.
There is nothing in those lower levels past where you were but an empty room where we figure the water dragon will go. You can get through that wall if you keep running into it with the arrow keys, you will pop right through.
If you were on ring 4, the doors you were looking at would go to the center (there's a big spire you can climb there). Not all the doors to ring 5 open.
Once you're in ring 5, the center of the garden where the tower is, then yes the water door deeper down is not implemented).