What level is this?

[SaladStream]

I remember playing a level towards the back end of a megawad. Maybe 21-29. The map was a long rising 'staircase' which switched back on itself and you could jump down into the Lava surrounding at pretty much any point. Nearer the top it became covered like a tunnel still with stairs and each tunnel had revenants and hellknights that teleported in or came out of hidden doors. A bit similar to the end of doom 2 map 29 leading up the exit but it carried on for about 500 steps. Finally at the top I'm pretty sure there was a key then you had to go all the way back down to complete the level. Sorry not much to go on but this has been bugging me for weeks. I can't find the level anywhere.

[bonnie]

 

[SaladStream]

Thanks I'm new and didn't know there was somewhere separate for this