My rainbow nether hub and connecting tunnels are mostly done! Any suggestions for the exterior and a door to exit into the nether?

I've been building nether tunnels in my world for a while and just finished the interior of my nether hub. I'm pretty sure ghasts can't spawn inside (hopefully). I'd like to add a door to the outside somehow and make the exterior look nicer because it's currently ugly from below. Otherwise, I'm pretty proud of this build!

Also, the color of the tunnels are somewhat related to a destination in the tunnel:

• The red tunnel with crimson planks and nether brick leads to a Crimson Forest and Nether fortress.
• The yellow tunnel leads to a Bastion with my frog light farm and a future bartering farm.
• The teal tunnel leads to my Stronghold.
• The purple tunnel leads nowhere right now.