I was surprised by the intensity of the hallucinations that this video, Acid Trip Without Drugs! induced.
To get the most out of the video, stare at the center point on a laptop screen or larger and watch the full video.
The video itself will begin to warp after a while, and then when you look around the room everything will be growing and shrinking. The effect only lasted about 10-15 seconds for me, but they made me feel like Alice in Wonderland.