We make a dry landing at Sullivan Bay, Santiago Island and are going to walk on the lava flow there. The eruption took place 200 years ago and is of a similar structure to the Hawaiian eruptions called pahoehoe. The lava flows slowly and forms smooth humps. The lava has set in all sorts of weird and wonderful shapes.

The new lava field is black, in stark contrast to the ancient lava – maybe 2 million years old –  which it has flowed over, which is red and has weathered into rocks, shale and sand.

It is a totally alien landscape and we feel as though we are walking on another planet. Scrubby plants cling to life on the old lava flow and there are very occasional small plants just beginning to grow on the new lava field.

A crab seems out of place in this hostile terrain.

A fly catcher follows us as we walk. It is hoping to catch any insect that may land on us and as a result comes very close to us indeed.

The sky is cloudless and the sun beats down. It is searingly hot – probably well over 40C. We drink loads of water. I have taken two bottles and I need them. We are very relieved when 2 hours later we finally arrive at the beach.

I cannot take my shorts off fast enough and run into the sea. It is absolute bliss to swim in the cooling water. We have brought snorkel gear. The marine life is good. I see a sea lion, two turtles and lots of reef fish. Some people spot a couple of penguins but I was too busy looking at a large ray.

In the afternoon we snorkel at Bartolome.

This time we all see the penguins. There are only three but we feel lucky to have found them and no-one is in a hurry to get back in the boats.

The current was quite strong in places so we have had a good deal of exercise today. However there is more to come. We shall finish the day with a walk up to the top of Bartolome some 114 metres high involving 370 steps.

This in 40C heat with no shade and high humidity is a big ask but we all make it.

The older ones amongst us take more rests than the youngsters. I am so hot when I reach the top that I pour the remaining contents of my water bottle over my head and down the front and back of my shirt. Bliss!!

Back on board I down an ice cold beer, shower then return for a margarita and farewell briefing.

Our guide Fabian, loves snorkelling and has made a short video of our snorkelling trips. It is really good. He has a GoPro and his footage is much better than mine. That will be my next Xmas present sorted!