I like things that make me feel small.
Like If The Moon Were Only 1 Pixel, a “tediously accurate scale model of the solar system” that, as you scroll horizontally, reveals the vast span of our neighborhood:
Or Why Time Flies, a philosophical exploration of our fungible awareness of time:
Or The Scale of the Universe (my favorite), which, as you zoom in and out, shows the comparative sizes of all creation, from the largest supercluster to the smallest neutrino (notice how everything at some point is the same size):
Or Lightyear.fm, a “journey through space, time & music” that plays songs of the past according to how far their waves have traveled from Earth since they were released: