It kind of depends what you are looking for...
If you're looking for other psychoactive drugs to experiment and explore different aspects of your mind, reality, consciousness, etc , I'd recommend Ecstasy like soulcompromise mentioned and I also recommend Mushrooms/LSD like your friend mentioned.
Ecstasy might be appropriate as it tends to be less visual than Mushrooms and LSD, but it retains a lot of similar sensorial effects and I find the headspace quite unique and mind blowing. However it isn't as benign as Marijuana, it can induce some side effects such as jaw grinding and you can have a "crash" after, so there are certain precautions you should take if were to explore it.
I think the "Hallucinations" and visuals of Mushrooms and LSD for the most part are likely quite different then your preconceptions of it. I've noticed "It's different than what I was expecting" is borderline a mantra for people after their first trip.
If you just want novel ways to get intoxicated, I'd probably recommend Cocaine or Kratom. These tend to be less immersive than the other drugs I mentioned and therefore perhaps a bit more functional. They got some decent euphoria and with coke you can pretty much talk your head off and Kratom is a bit more chill.
I don't view any of these as "replacements" for weed though, eventhough I actually prefer Ecstasy, LSD, and Mushrooms. Alternatively you could probably pick up a hobby.