Mynydd, pronounced munith, is welsh for mountain. I spend my days surrounded by mountains. The stitch panels remind me of mountains, the hills in Wales just keep rising and falling, just like the stitches in this pattern.
At the heel you manipulate the stitches to change from being big mountains to smaller hills.

The charts for the twisted stitch panels look complicated, but the actual stitch pattern is simpler than it seems. You’re only ever crossing each stitch over its next-door neighbor. As long as you keep working the knit stitches through the back loop it will all work out. If you’re struggling to follow the chart, have a look at the written directions, and compare your work to the photos of the panel.
I recommend using a semi solid or tonal yarn for this pattern or your risk loosing definition of the stitch panel.
Size small fits an average female foot, and size large fits an average male foot.