I was watching ol' Dave Rupert play around with horizontal layouts in CodePen the other day. He found something that I wasn't aware of. A CSS trick, if you will.
When you're using CSS columns, and you set the column-count, say, to 2. The content will be split up into 2 columns in the visible area. It doesn't mean only two columns period. If the content overflows that element (easy to do if you have a fixed height), more columns will be created horizontally. Plus you can make that overflow scroll.
I'm sure y'all smarties out there could make it even cooler with like snap-to-scrolling (so you don't get in-between columns scrolling), progress indicators, localStorage saving position, @media queries for when to go up or down in column-count, all that kinda cool stuff.