In the Chapter: Glimmerdimm Beach, you will speak to a large fish-like creature. After that conversation,
continue forward and you should notice large jelly pads on the ground that you can jump on. They will
propel you into the air, high enough to land on the archway above the waterfall. You will need to double
jump and use your guitar for a little extra height to make it onto the archway.
See the video below for all non-story related achievements.
0:00 - Light It Up Achievement (Chapter: Tuning Into A New Dimension)
2:32 - Stage Fright Achievement (Chapter: Into The Heliotromms)
3:08 - Snowman Achievement (Chapter: Into The Heliotromms)3:33 - How'd You Get Up There Achievement (Chapter: Glimmerdimm Beach)
4:05 - New Threads Achievement (Chapter: Frida's Closet)