Vitis Begins moving down the tunnel very slowly along the edge, stopping the moment he sees the dragon. (Vitis is currently invisible.)
You can see a colossal red dragon and... a huge humanoid with large wings on it's back tossing spells at the dragon. This humongous cavern has a ceiling 600 feet up and walls 1200 feet apart. There is a waterfall made of lava on the back wall, it provides adequate light to half the cavern and shadowy illumination to the rest.
If you don't know what the the humanoid is: knowledge (the planes) or knowledge (arcana).
I do all of this on my phone... I'm sorry if I'm slow or miss a post.