Geyser Sol de Ma̱ana Рat around 4900 metres altitude, it was the highest point we reached throughout the trip.
People lurk in the steam of the fumaroles. We could wander around at will in amongst the geysers, fumaroles and mudpots, with just common sense stopping us from going in silly places. As a result I nearly slipped into a mudpot (the mud was unexpectedly slippery and wet! I was taking photos! There were no safety fences or signs, how was I supposed to know it was dangerous!? *shakes fist at the world*).
The terrain was very Mars-like, with geysers in a mixture of different colours (including bright red, due to high iron content perhaps?).
There were lots of little plib plobbing mudpots, bubbling merrily away, some more enthusiastically than others. I could have sat and watched them for hours.