YouTube's exploring functionality in the full-screen video player allows users to directed exploration of related videos.
1) Clicking the explore button in the lower left brings up related videos visualization, which is sort of like a digraph that looks like a constellation of stars.
2) Circles in the center are videos. Hover over one circle expands to show you other videos related to that one, forming a cluster. Click a circle to watch a video.
3) Circles in the upper left corner indicate the clusters you've explored. Clicking on a circle returns you to the related constellation, focused on the cluster you click. Constellation shows the path back to the original video--what relates the video you're now watching to the video that started your exploration.