Use it for what you will but this is my 4-way splitter dome for my train system. It has power rails running thru with hidden redstone torches under rails. The 3 ports leaving out with the single track system will match both of my bridge designs in my other uploads.
Entire bottom half is filled with water with handrails for spectators. Main intentions for this is for people who use any type of aquatic mods to spawn fish and other water creatures to add some visuals.
You'll notice when you paste this there are some random signs inside aswell as pieces of fence at each entrance. This was my only structure with lighting for awhile so all animals kept coming there, so I had junk fences coverig the entrances lol.
Structure is 57 long x 57 wide x 25 tall (from ground up)
Water is 5 blocks deep with quartz bottom.
It's copied at ground level and will place perfectly