Thailand's Khao San Roi Yot National Park – or 300 Peaks National Park – is on the coast near the beach resort town of Hua Hin, three hours' drive south of Bangkok.

The 98sqkm sanctuary is full of wildlife, mangrove swamps and its signature limestone mountain peaks soaring skywards in a series of jagged, sculptured ridges.

The ride in a cheap cab 60km south from Hua Hin to get there was a pleasure.

At a stop at Khao Ko Lok, a small traditional fishing village, colourful boats bobbed in the shelter of the bay while women sitting under shade trees picked crabs from nets.

A temple and monastery were nearby, and the locals were quite happy to chat with us as they went about their daily business.

From here, the peaks of the national park began shooting up from the flat paddocks like office blocks erupting from plazas. Winding our way through, we ended up a little further down the coast where another fishing village with thatched beachfront cafes was our stop-off point for a hike.

A rough rock stairway led up a cliff, skirting a mountainous headland to reach Laem Sala beach on the other side.

It was steep going up and steep going down but gave sensational views of the coast and nearby islands, including Young Lady Breast Island, responsible for a nearby resort being named Brassiere Resort.

A walk through a shady grove of trees fronting the deserted beach on the other side led to signs saying 'Go To Cave' – which sounded like an order to be obeyed, so we did.

The track through the rainforest led to another path 450m up a steep mountain, so steep that we met an older couple coming down who had given up.

We pushed on, sweating in the tropical heat, past a squealing troop of monkey-like lingurs, staying ahead of a group of immaculately dressed Thai children on a school excursion who constantly giggled and called out "Hello, hello".

A lookout revealed sweeping views over the hinterland, before we pressed on gamely towards the top.

Here, the cliff wall suddenly opened to reveal odd sights: through a large tunnel were boulders at crazy angles, a suspended 'waterfall' of stalactites, eroded walls and what was once a huge cave chamber.

A gaping hole in the roof 100m above now lets in light, allowing a hidden garden to grow in isolated silence.

This Lost World was impressive, but more was to come.

Following a tunnel called the Crocodile Back Walk – the 50m path is along craggy rocks just like a croc's back – another massive chamber known as Tham Phraya Nakhon came into view.

This dome-like chamber, the size of a football field with walls rising several hundred metres, also has lost part of itsroof.

As you enter, shafts of sunlight shine on an extraordinary sight. King Rama V was so impressed with the cave that in 1890 he ordered a royal pavilion be built.

The sun shines down to illuminate this temple-like structure, adding an eerie sense of awe to the place.

The chamber carries the silence of a holy place – so much so that even the boisterous schoolchildren who followed us had their chatter reduced to subdued tones as they took in the wonder of the place.

You can wander around the chamber taking in sights such as the Crocodile Rock, the Love Tree, wild gardens, several small buddhas, rock columns and hundreds of sticks placed at 45 degrees against the walls by previous pilgrims.

After placing our own sticks we made the trek back down the mountain and around the steep rocky headland before finally flopping for cold drinks at the waterside thatched huts.

Several kings have made the journey to gaze at Tham Phraya Nakhon. For king or commoner, it is an unforgettable sight.

The writer visited Thailand courtesy of Flight Centre and Tourism Thailand

The Sunday Telegraph