You should fill the space between the floating temple (which should be cast out of obsidian) and the scorched earth below with ornate glass pillars that spiral up to the base of the temple like helixes. The pillars should be hollow, and filled with magma so that they glow with an unceasing red light that makes the earth below appear eternally shrouded in sunset. These should have stairs or ramps encircling them that form a narrow path, so that on them your dwarves can fight off invaders who try to reach the black heights above.
The temple itself should have an arched ceiling, and underside of which is a great mural made of a mix of different colored materials, perhaps of a magma flood destroying the enemies of the dwarfs. It should be built in a circle around the volcano, and be connected to it only by 1-tile wide walkways that can be caved-in at the pull of a lever.
The facade of the temple that faces out from the volcano should be lined with statues and pillars, with hidden niches from which archers can emerge and open fire. The inner facade of the temple that faces the volcano should be lined with the cages of those who will be devoured by the flames, in full view of the magma falls that they will soon be thrown under. In between might dwell the blood priests themselves.
If you can, also line the sides of the volcano with glass spheres filled with magma; maybe even have glass tubes running off from the sides of the volcano with magma-proof hatches on their bottom so that they can release magma on the enemies of Armok below.
NON-DESIGN NOTE: if you don't see any goblins in the "c" civ screen on embark, they might still come as the game doesn't list civs in Fortress Mode that you haven't met yet; also if you take your world gen parameters and regen the world, but stop it a little earlier, you might get goblins before they die out, and you can then find this original location again.