Zero Gravity in Gold and Black Sapphires

The day started slow paced, even though we were going diving, we didn’t have any rush, and on these situations, it’s convenient to double or triple or quadruple check everything, and take with you as many spares as you can!

First good sign that the day was going to be good, crystal clear water.

The preparations started the day before, it took us about 3 hours to put together two full sets of equipment, including gas fills, analyzing and all checks. One of the nice things about diving GUE is that we can arrive at the dive location with only our pigtail with cookies and arrows, and we are sure that our buddy will have all our usual gear for us, as standard configuration. On the day to the cave, drive, coffee and start with the usual site check and topography review. On the way to the cave, we talked about plans, what’s the main goal for the day, obviously HAVING FUN!!, but to have some others in mind, we wanted to assess different video possibilities along the cave, to be prepared for our next projects.

Alviela provides nowadays 10% of the consumable water in Lisbon, and it is one of the biggest aquifers in Portugal. The area is also known as picnic and family area, with plenty of visitors during the summer to calm down the hot temperatures in Central Portugal. It is located between the Estremenho Karst Massif and the Tertiary Basin of Low Tajo. There are close to 140 million years difference between each of the rock systems. They are dated from the same orogeny that formed the Alps and the Pyrenees. The cave systems in the Massif are being documented as part of a Project Baseline initiative.

The entrance to the cave, already a two passage system.

First, site survey: before starting to gear up, we needed to check the site status, like water level, way to the cave (for me) and possible water flow: which is  not common in summer time, of course, but it is something always to be checked.

I have never been there, so it is mandatory to check the procedures and ways to gear up, carry all the gear to the cave, and usual tricks that only locals could give you.

To enter into the wet cave, you need a couple of ladders, specially if you’re going to carry gear, I don’t see how can I climb a bare rock with my twinset on the back! Thanks to the people at SPE, everything is organized with the ladders and tools to safely access the cave.

Access to the water

My first cave dive after GUE cave 1 class in Sardinia!! I was super excited!! We were a team of two, and we planned gas (double thirds) to do three dives on the cave. The first dive would be just to get a first impression for me of the cave, and to make up the topography of it in my mind, get used to the change of depth and smoothness and get some waypoints. That was not the case for my buddy, who knew each of the cracks that you can find there, but both of us needed to have that clear idea of the topography.

We started to carry all the gear, so it was ready just for when we got into our drysuits and jumped in the water.

Gear ready!

After gearing up and the pre-dive checks we descended into the tunnel which gives entrance to the cave, following the main line. The beginning of it is a wide and tall tunnel, which starts to get deeper with a very smooth slope. As happens with a lot of caves, your brain can’t really imagine what’s going on just by reading the topo, specially the diving technicalities.

Tunnels naming with depths

Suddenly you realize that you are swimming in golden walls, with black cracks all along it, which look like black sapphires crusted in gold. The cave splits into two tunnels in 30 meters from the entrance, but they are not independent, they are connected through windows, which give a lot of room for imagination to play with lights and have some unique scenarios for photography.

Tunnel A top view

We had a depth limitation due to gas (32%) and to deco of 30 meters, so we concentrate our dives on tunnel A. within GUE C1 limits, and after three 50 minutes dives, I would say, it is still not enough time to “explore” it all, if you really want to enjoy its colors and features. The tunnel has a couple of jumps on it, towards other passages, but we’ll keep those for other dives. I entered the cave with my eyes wide open and all my senses alert, as you do anyway when you go into the unknown, it doesn’t matter how much brief or study you do before.


When we reached the -30m depth limit we turned back to exit, following the main line, and sloping back up to the entrance. The feelings that you, or at least I have before diving a new cave are always a mix between vertigo, excitement and curiosity, and that remains on the way back, as you have a complete different view of the cave, with a new perspective. That famous knot on your stomach remains until you take the first breath of uncompressed air out in the surface.


After some surface discussion and a questions, mainly from my side, of course, and first impressions, we started the pre-dive checks again and went back. The goal this time, was to record some footage of one of the side passages, to build a 360 degrees virtual reality video of it. Also, we needed to figure out how to play with lights, and get some good photos for the project that is coming up next September, more information here

Start of the windows passage

On the second dive, as I had in my mind a general overview of the topology and some way points, I couldn’t resist just to enjoy it and keep on blowing my mind up getting the personality of the cave. The visibility was of 30 meters at least, having the feeling of flying on it. It is a rather dark cave, so the illumination is a bit more trickier than for example caves in Mexico, it absorbs most of the light, making illumination a challenge. Playing with the windows and lighting, we got a clear idea as well on what to improve for next expedition.


Before the last dive, we took a break from the cold water, and went to the daylight for some time. I can’t really described the feeling of going from a completely dark and peaceful atmosphere to mid-day sun and kids playing on a pool in summer. After having a breath, we went back into the cave, ready to fill up our twinsets with some spare tanks we brought, so we could have them top up for the last dive of the day.


Being the third dive, I already had on my mind way more waypoints and the cave topography so I could focus on lightning and some new ideas to take footage. We went back to the -30 meters range, trying to get a long clip with different angles, so we could trace some strategies next time. It turned out to be one of the most amusing cave dives I’ve ever done, what it was going to be a short dive to wrap up some of the shots turned into 47 minutes of darkness and brightness, peace and giggles.     


Dive technicalities

  • Coordinates: 39.445617, -8.712091  
  • Dive 1
    • Dive time:  28 minutes
    • Max depth: 29.6 meters
    • Average depth: 15.9 meters
    • Gas: 32%
    • Water temperature: 17 degrees
  • Dive 2
    • Dive time: 31 minutes
    • Max depth: 24.6 meters
    • Average depth: 14.0 meters
    • Gas: 32%
    • Water temperature: 17 degrees
  • Dive 3
    • Dive time: 47 minutes
    • Max depth: 29.5 meters
    • Average depth: 15.1 meters
    • Gas: 32%
    • Water temperature: 17 degrees

More information:



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