Acid can be an incredible experience if done with the right people, with enough stuff to do and a couple of days spare. As said, 12 hours can drag on, and it can be quite exhausting, particularly if you have spent 8 of those hours laughing harder than you have ever laughed in your life - believe me, laughing can become torture! That said, those sessions often end up very cleansing and life affirming in the days / weeks afterwards.

Mushrooms - I have had 50/50 good / hard experiences with them, the nausea tends to drag me down a bit. But the good trips II have had have been fantastic. I too find them to be very 'nature' oriented, so if you do decide to go this route, make sure you have grass to roll on, trees to climb / hug depending on your style, and dose low to start off with just to get a feel for them.

DMT - the king of psychedelics in my opinion. Just... WOW. But, better suited to exploring either on your own or with maybe 1-2 other people who know to keep their mouths shut while you are journeying deep. I am less inclined to recommend this substance to people who aren't used to psychs because it is SO weird and can be absolutely terrifying. On the other hand, pure bliss, basking in God's glow etc can be quite the opposite. Approach with caution and respect, more so than the others, even though the duration is far shorter (unless taken orally)...

What ever you choose, good luck, I am sure you will be dazzled by any and all of these