Old "modern hardwood floor", thought it should be easy. Get drum sander, off I go. Except the sander hire person was kind enough to point out that the old varnish would "shine up" belt after belt, and I'd probably want to chemically strip it first.
And that's where I draw a blank! What's the right stuff? The only relevant result I get when googling is actually offline at the moment, but here's google's cache of the page: