Wat Saket temple, also known as the Golden Mount, is set on an artificial hill. There are about 300 steps leading to the top, but the slope is not steep and it's worth taking since there are serene hanging gardens with tropical plants and artificial waterfalls and ponds along the way.
Wikipedia https://th.wikipedia.org/wiki/พระบรมบรรพต
Coordinates 13°45'13.865" N 100°30'23.837" E