Lamru national park is just 6km from Khao lak and easily reachable with a taxi (250baht).
My original plan was just to visit the nature trail which is only few km long. The trail surprised me by being quite varied with small climbs and descents. The best part was the amazing little cove with a beach towards the end. Dip in the sea was perfect ending for the walk!
To reach the waterfall from the parking you first have to walk 1km on a dirt road mainly uphill after which you reach the lower part of the falls. The falls are actually in 5 separate levels and in total more than 100m high meaning if you want to see the entire fall you have to hike much more on the path on the side of the waterfalls. But it was definitely worth it!