Best for the "what is this" reaction.
For peak strange-by-effect impact:
This Person Does Not Exist — refresh for a new AI-generated human face. None of them exist. The technology is GAN-based; the cumulative effect is unsettling in a way that doesn't get old. Built in 2019 by Phillip Wang on top of NVIDIA's StyleGAN. The unsettling quality has only grown as the technology has improved.
InspiroBot — AI-generated motivational posters. Click to generate. The outputs range from accidentally profound to actively threatening. The bot has its own dedicated subreddit; the best outputs end up in art galleries.
Ever Dream This Man — a 2010 internet mystery. The site documents a face that thousands of strangers worldwide claim to have seen in dreams. The "investigation" framing is sober. The premise is uncategorizably strange. Subsequently revealed to be a viral marketing project, but the site remains as documentation.
ZomboCom — a single Flash animation (now HTML5), launched in 1999. A spinning pinwheel and a deep voice intoning "the infinite is possible at Zombocom." Has been continuously online for over 25 years. The voice still sounds the same.
MapCrunch — drops you at a random Google Street View location anywhere on Earth. Click "Go" and you're somewhere. Could be a Mongolian highway, an Argentine suburb, a Norwegian fjord. The lack of context is the experience.
These five reliably deliver the strange-by-effect register inside thirty seconds.