This is a a small national park not far from Rayong. It has a waterfall which has endless opportunities for trekking, some of it quite steep and adventurous. There is a campsite at the foot of the waterfall near park headquarters. It is surprisingly rustic, given its close proximity to the eastern seaboard. It is really worth considering as a a quick break from Bangkok, and does not attract the visitor numbers of Khao Yai. I wouldn’t go far out of my way for the place, but it definitely is worth a trip from Pattaya or Rayong, or if you are looking for an overnight camp on the way to somewhere. Probably, like all national parks, best to avoid this on high days and holidays.
It appears that the park authorities at Khao Chamao actually come to work in the morning, and have placed litter bins along the trail, so you may find that there are fewer water bottles and styrene containers decorating your trail than you would expect in a “minor” National park. Congratulations to the powers that be at Khao Chamao!