There are 18 caves within the 478 metre high Gunung Senyum ('senyum' means smiling in Malay). Estimated to have been formed about 400 million years ago, this limestone outcrop, passed off as a 'mountain' in these parts, comprise two other giant geological protrusions, namely Gunung Jebak Puyuh and Bukit Terus. Gunung Senyum, with its complex of caves, including Gua Angin, Gua Terang Bulan, Gua Taman Satu / Dua, Gua Makam Tok Long (a burial cave) is the most popular as it is easily accessible. Some of the caves are archaeological sites that are still being excavated by archaeologists. Besides evidence of prehistoric human existence in the area, the interesting story surrounding Gua Makam Tok Long is noteworthy for its unworldly colours.

According to the locals, Tok Long was a pious person who once caught a spotted dove using golden feathers. One day the bird escaped, and while Tok Long was looking for it in the jungle he came upon a colony of fairies with whom he stayed until he eventually married one of them. When one day he longed to return to his village, his fairy wife said that he could only do so if he promised not tell anyone about her. Upon agreeing to this condition, Tok Long went home. No sooner had he arrived that he was bombarded with so many questions. In the excitement he accidentally divulged his secret. He had broken his promise and when tried to go back to his fairy wife, she could not be found. Hence, broken-hearted Tok Long went to a mountain and spent the rest of his living days meditating in a hole he dug. The spot where he died is known as Makam Tok Long.

The are two popular tales pointing to how the place got its name. One is about a duel between two Malay warriors that ended in the death of one of them - smiling! The second version allegedly took place between 1863 and 1892 when the then Sultan Ahmad of Pahang was travelling to Kuala Krau in Temerloh. It was said that when he saw the mountain, he asked his men if they knew its name. Not knowing, the men looked at each other and just smiled. Realising no one knew the name, the Sultan proclaimed that it be named Gunung Senyum

Cave exploring, rock climbing, jungle trekking and camping are the main activities at the Gunung Senyum park. It takes about two hours to climb Gunung Senyum, and nearly a day to visit the caves. The trails into the caves are challenging as some will require visitors to crawl and climb using ropes. Gunung Senyum is, therefore, off limits during rainy season and at night. The hill and its surroundings, including most of caves are part of the Gunung Senyum Recreational Park, which is under the 794 hectares Jengka Forest Reserve.

A recent news that is disturbing to residents in the area are plans to approve a limestone quarry next to Gunung Jebak Puyuh. If this materialises, this pristine environment will be threatened.

There are chalets as well as a traditional Pahang house built in 1907, which used to belong to Datuk Setia Amar Mohamad Yassin Stan, one of Pahang's noble men. All cave excursions must be guided. Please enquire from the ranger's office for guides.