Half a tab of LSD can get you there and keep you there for hours.

BRB, trying.

Weed could do it. Other things too, but weed is always a good first stop for nice mind effects.

Honestly, I've experimented a lot with mind altering substances and that was something quite different.

And then a dozen others will jump in saying that regardless of the actual authenticity of the experience it doesn't count if you did it by directly altering brain chemistry rather than indirectly altering brain chemistry.