I built the center, and I used a carpenter's trapdoor from Carpenter's Blocks, which I used an alternate iron block as the cover thanks to Chisel, the trapdoor leads underground to the maintenance room where the mentioned Serenade of the Nether operates when the mana pool isn't full. And thanks!Impressive asthetics. I really like the hydroageas and theralily farms.
On the thermalily farm pic, is that metal grate a trapdoor?
Also, your treehouse has a regular giant tree at the center, or did you build that was well?