Well that was fun. Even though I was in (I think) the fourth group, the tour into the hot spring (Fuente Santa) started bang on time. First there was an audio visual presentation, then we put on the hard hats and went down the tunnel. The guide pointed out the various places along the route where we were going through either solid basalt lava, or porous volcanic rubble.
Along the tunnel there are various side pools. Most of them have mineral salts floating on top, and each is at a different temperature. The water level, temperature and composition depend on the tide outside – seawater flows in as well as spring water flowing out.
In the end pool, I finally got to do something I’ve wanted to do for at least 20 years – I dipped my toes in the water from a thermal spring. It as warm as a good bath, and the water felt slightly oily with all the dissolved salts. So that’s me happy.
The amount of gas in the tunnel varies, depending both on what the volcano’s burping out and how much wind there is outside. They have lots of gas sensors and a good ventilation system, and I’m sure it’s safe. But after a while you get a gentle prickle at the back of your neck. When we left an hour later, I really fancied a beer.
Luckily the restaurant and café at the salt pans is only five minutes drive away. They do local craft beer too.
UPDATE: Apparently over 100 people went to the first open day. One of them was Steve Simpson, an artist who was invited by the Tourist Board to come to La Palma as part of #onthedraw. You can see his illustration for the Fuente Santa at http://sheilacrosby.blogspot.com.es/2014/07/the-spontaneous-guide.html
Sounds like a good experience.