Altavista used to work like that. Even back when Google was still cool I hopped back to good ol' av.com just to find exactly the thing I wanted.

I miss the old cluster graph that AltaVista was rolling out right before they died.

I could search something like "trek", see that there were several very different clusters (one big one for science fiction; one big one for outdoors; and a smattering of smaller ones), and select the cluster I wanted to drill down into.

That should be even easier to do nowadays. Sadly, that seems to get in the way of irrelevant ad clicks, so nobody seems to have picked it up.