The always-excellent Vi Hart (previously) gives one of the most engaging explanations of multiple infinities we’ve come across in some time.
https://gizmodo.com/meet-the-hexaflexagon-its-about-to-blow-your-mind-5947852
Complement with our brief but thorough introduction to infinity.
https://gizmodo.com/a-brief-introduction-to-infinity-5809689
H/t TMS