The raptchen

So i thought really hard there's fire kind of dimension(nether) there a sky dimension(end) and there's basically a water dimension(ocean/ocean monument) so i thought " hey there isn't an underground dimension" where its all blocks but when you get there your portal is surrounded by cobblestone exactly 5 blocks away from the portal 6 long and 7 up so when you its a bunch of blocks in the way and you keep digging until you find these structures called runes witch are just underground spawners but except there no spawners and instead of cobblestone it Blackstone and also there are 4 hidden chest you must but be careful where you dig there lava where you might dig and i don't wanna make this a too op dimension so basically to make the portal and also i wanted to give diorite some shine cause people never use it so maybe use polished diorite in a 4 up by 3 long and to activate it maybe by putting lava in it from the top and of course i need mobs so maybe bats that spawn in the random genera holes,(2 high 2 long 2 across) and a very very very like 0.01% a wandering trader will spawn and a only a 30% chance of finding emerald ore and 1 more thing we need a mob to Guard the runes so I've chosen witches they are perfect for the job maybe 1 or 2 for each rune.