Hallucinations are an interesting thing. I've gone as deep as 4 tabs of pretty strong and clean stuff, and never seen anything that wasn't there (like a pink elephant appear and walk around). I have had some "internal" hallucinations where I was in an entirely different place and detached from reality, almost like an extremely vivid daydream. Then I've also had some very detailed CEVs.
The "internal" hallucinations were interesting. In one I was suddenly back in my preschool at the YMCA, and kind of flew around a bunch of places related to it, then it all turned into a monochrome cartoon mime/clown face which melted and I snapped back to reality. It really felt like I was there, and it kind of freaked me out a bit, but it was a good trip.
Another time on mushrooms I was listening to Phish playing Reba with my eyes closed. In my head I was suspended in the sky, no land around, observing this enormous harp like structure that was rotating and playing the notes (during that pretty soft ascending middle section of the song), as it rotated it was moving upwards leaving walls behind them building a spiral structure. As that section peaks and the music descends in a tumbling manner, the entire structure fell apart and started to fall. This felt similar to the pre-school thing, but I was laying down with my eyes closed.
As for melting, I've had this effect in some stressful situations... like being in a hotel elevator on some strong acid in NYC w/ some girls who looked like crackheads (but were actually nice and understood what I was feeling), and a friend who was upset that I didn't want to hit the bars after the show. The walls weren't literally melting away to reveal something else, but they did appear to be running towards the floor.
Other than that, usually I get the typical wall-breathing, color shifting, and time dilation with both LSD and shrooms. But LSD is far more visual for me, w/ lattice type overlays, pattern recognition (looking at bud is
), and occasional synestesia.