1. We did the optional Inca Trail day walk to Machu Picchu. We alighted from the train directly down onto the track, no platform of any kind, and just the 4 of us (including our guide). Everyone else on the train continued to Machu Picchu. We were in some remote jungle next to the river and as we crossed a footbridge a flock of parrots screamed overhead - I felt like Indiana Jones! We saw hardly anybody else on the trail. Not counting our guide, my wife was the youngest at just 59 and our excellent guide, Juan-Manuel, paced our walk gently so we took 6 hours of steady climbing to reach the Sun Gate and get our first view of Machu Picchu. I was literally moved to tears.
2. Snorkelling in Galapagos. A group of 4 or 5 sea lions joined us just to play.
3. The tameness of everything on Galapagos. Having to walk around Boobies and Albatrosses because they don't get out of your way - in fact they are more likely to come closer for a good look at you.
Altitude: This affects people differently. I knew people who have done this trip before and was told I would have a headache on the first night in Cusco and perhaps feel nauseous. I was a bit concerned because I know from previous experience in the Alps that I don't do altitude well. However neither my wife or myself experienced either of these symptoms but I did feel a little short of breath at times. This did not impact at all on our ability to enjoy any of the trips or activities. More surprisingly I had most trouble with the breathlessness when trying to sleep.
Inca Trail: For anyone used to a little hill walking in the UK, pennines or lake district for example, it is no problem. But don't get fooled by references to "short" trail. It is only short compared to the 4 day hike of the full trail. We took it pretty steady and it was at least 6 hours of steady uphill walking.
Cachalote (the boat in Galapagos): The boat is quite small and the cabins are tiny but the bunk beds are comfortable and ensuite toilet and shower facility are fine. There is no opulence here (none wanted either). We had 2 large suit cases which were difficult to deal with in the small cabin. Most travelling is done at night and it can be pretty rough. The food is simple but excellent and generous.
Snorkelling: The water is quite cool. I have no wet suit and elected to do without (available for hire), making do with a couple of tee shirts. If you can swim in UK water you'll be ok as I was, it is a bit warmer than UK, although I was coming out with numb fingers after an hour in the water. The Americans on the boat used wet suits and they were complaining of the cold!