Exploration of Sintzi Spring, the deepest cave of Greece

Sintzi Spring (Greek: Πηγή Σίντζι) is the deepest explored underwater cave in Greece, located among the picturesque mountains of the Peloponnese.

Our first encounter with the cave took place in May 2023. We spent a week diving in Sintzi, learning its layout and investigating potential leads for further exploration.

The morphology of the cave is particularly interesting, with numerous junctions, side passages, winding corridors and two deep shafts. According to the information available to us at the time, the first, relatively tight shaft had previously been explored to a depth of approximately 94 metres, while the second, much larger shaft had been explored to around 186 metres in 2015.

First expedition – May 2023

During our dives in Sintzi, with support from Mariusz Banaszak, I managed to reach the end of the existing guideline in the first shaft at a depth of 94 metres. It quickly became clear that the cave continued beyond this point, but there was an obstacle: a tight restriction. I managed to squeeze through it using my backmount Liberty CCR, but the passage was uncomfortable enough that I decided not to continue farther on that dive.

We now had confirmation of at least one promising lead for future exploration — an inviting, unexplored corridor with no guideline disappearing into the darkness.

The final days of the expedition were focused on the second and much deeper shaft. Over several dives, we repaired damaged guidelines, staged bailout cylinders and gradually prepared the route for a deeper push. On the final dive of the expedition, I descended to a depth of approximately 170 metres. The shaft continued vertically below me, with no bottom in sight.

That was where the 2023 expedition ended.

Returning to Sintzi – May 2024

We decided almost immediately that we had to return the following year.

In May 2024 I was back in Arcadia, although with a different team, as Mariusz was unable to join us because of work commitments. This time the objectives were considerably more ambitious:

Pass the restriction at 94 metres using a sidemount Liberty CCR and explore the corridor beyond it, laying new guideline.
Reach the existing end of the line in the main shaft at approximately 186 metres and, if the cave continued, begin exploring beyond it.

During more than a week of diving focused entirely on Sintzi, I completed several preparatory and conditioning dives, staged open-circuit bailout cylinders and repaired damaged guidelines in the deeper sections of the cave.

Then it was finally time to explore.

Beyond the restriction

The first objective was the corridor behind the restriction at 94 metres. Passing the tight section — visible in one of the photographs in the gallery below — was significantly easier using a sidemount rebreather than it had been with a backmount CCR the previous year. Within about 20 seconds, I was through and ready to begin exploring. With a reel in one hand and a Seacraft DPV in the other, I set off into an unknown section of the cave. The passage was wide and continued steadily deeper.

On the second day of exploration, at a depth of approximately 160 metres, I suddenly saw a guideline ahead of me. It took me a few seconds to understand what had happened...

The corridor I had been exploring had connected with the main shaft leading into the deepest known sections of Sintzi. Before reaching the connection, I had laid more than 100 metres of new guideline.

The two deep shafts were now connected.

Towards the bottom of the main shaft

With the exploration of the first shaft completed, I still had several days remaining to focus on the deepest known section of Sintzi.

After a day of rest, I returned to the cave with one objective: descend farther down the main shaft. One dive was not enough to reach the bottom, but what I saw was more than enough to make me return the following day. At approximately 180 metres, the bottom of the shaft finally began to appear beneath me. I could see a small dark object where the guideline terminated. It was the reel left by the previous explorer. But something several metres to the side was even more interesting. There was a large dark shadow in the wall.

And a shadow like that could mean only one thing: an opening. Possibly a corridor.

The lead at 190 metres

The objective of the next dive was clear: reach the reel at the bottom of the shaft, at around 190 metres, investigate the dark opening in the wall and, if it proved to be a continuation, secure the existing guideline, attach my own exploration reel and recover the old reel that had been lying there for nine years.

When I reached approximately 190 metres and directed my light towards the wall, the answer became immediately obvious. There was a large passage behind it.nThe cave continued.

I secured the existing line, attached my reel and prepared the route for the final exploration dive.

After approximately five hours underwater, I was back on the surface, already planning the final push.

The final push – 240 metres

For the final dive, I set myself clear limits. I planned to spend no more than seven minutes at maximum depth and inside the new passage, with an expected total dive time of approximately six hours. If the passage continued deeper, my absolute depth limit would be 240 metres.

After reaching my reel, I checked the Liberty Sidemount CCR that I was carrying as bailout and immediately switched my Seacraft DPV to its highest — ninth — gear. At that setting, I was moving through the cave at approximately 60 metres per minute.

Fast.

Visibility was excellent, and the passage continued ahead. After roughly three minutes of exploration, I had already passed 230 metres of depth, but the corridor was still going. I felt good. My mind was clear and I had no noticeable symptoms of HPNS. I decided to continue for another 30 seconds and then turn around.

Ten or fifteen seconds later, the passage began descending again. My dive computers showed:

240.0 metres.

That was my limit. I turned around immediately, cut the exploration line and began the journey back. During the ascent, I collected the staged bailout cylinders and eventually met Jacek and Agnieszka Strejczyk at one of the decompression stops. I signalled that everything was OK and showed them the maximum depth recorded on my computers.

Agnieszka took an amazing photograph of me there.

Several hours later, after a total dive time of approximately 6.5 hours, I finally surfaced. Michał and Beata were waiting on the shore in case any additional support was needed.

More than 250 metres of new cave

During the final dive alone, I explored more than 150 metres of previously unknown cave and increased the explored depth of Sintzi to 240 metres. And the passage still continues.

Over the course of the entire expedition, with the support of the team, I laid more than 250 metres of new guideline, discovered a connection between the cave's two deep shafts and extended the explored depth from approximately 186 metres to 240 metres. It was an exceptionally productive and fascinating expedition.

All of my exploration dives were recorded, and the resulting film can be seen below. Make sure to check it out.