Most people associate Thailand with beautiful beaches, exotic cuisine, and reef diving. Yet, despite many having heard of the 2018 Tham Luang cave rescue, few are aware that deep inland, there are many other very deep and rarely explored caves. Some of these are among the deepest caves in Asia.

In the Krabi province, one of Thailand's most popular tourist regions, there are many limestone caves of varying depths, including the Sra Keow system, which became known after years of exploration determined its depth at 240 meters. In 2007, Ben Reymenants, a technical diver from Belgium and later a member of the Tham Luang rescue team, successfully reached its bottom.

In 2015, Ben returned to Sra Keow to attempt to connect two parts of the system by performing a traverse – surfacing via a different route than the entry. For such a deep dive, this would mean the need to set up stage bottle depots for decompression on two different routes, undoubtedly a logistical nightmare requiring many deep dives.

To avoid this, Ben decided to use a very specific configuration consisting of two rebreathers mounted on one harness and twenty-liter stage tanks. This complex and heavy configuration required the use of quite unusual and ingenious solutions, such as using a buoyancy bag designed for sidemount configurations to control trim.

During earlier dives to a depth of 240 meters at the same location, the significant depth and long bottom time caused Ben to experience symptoms of HPNS (High Pressure Nervous Syndrome), which is very dangerous due to its impairment of psychomotor skills. To prevent this, during the traverse, the diver used a mix with a very high helium content.

Descending to the bottom, Ben followed an old guide line laid by Matt London in the 1990s, but from a depth of 85 meters, he was on his own.

Descending into the black abyss of the shaft, the cave walls gradually change from jagged, sharp rocks to smooth and polished surfaces. The color of the rocks also transitions from light gray to completely black, which, combined with the poor water visibility, intensifies the feeling of diving into the abyss and increases the psychological pressure on the diver.

During the descent, Ben met with his safety diver, Don McFadden, who passed him an additional tank just in case.

At a depth of about 200 meters, Ben reached the end of the guideline he had laid during previous dives. Before starting the actual traverse, he checked his overall condition and began the bottom phase. Despite the difficult conditions, this phase went smoothly, and during the ascent in the second shaft, Ben was joined by Ralf Wagnersen, the second safety diver, who accompanied him during the shallow decompression phase. The shallowest (and longest) part of the decompression was performed using open circuit and pure oxygen as a decompression gas.

The dive was not only a great mental burden due to the overwhelming environment and poor visibility but also a huge physical effort. The high task loading during the dive and a back-mounted setup weighing 95 kilograms could exhaust even the best-prepared diver.

What affected Ben the most during the dive were... shrimp. These small creatures inhabiting the entrance wells incessantly tried to get to every piece of exposed skin, "enriching" the long hours of decompression in an unforgettable way.

In the end, Ben Reymenants returned to the surface safe and sound after completing the deepest traverse of a flooded cave in history. The only thing that was not achieved was taking photos of the dive itself. The very poor visibility practically made it impossible to take any underwater photos.