I once stayed at Play de las Americas and noticed this mountain next to the city, decided to go for it one morning. It looked "runnable" for me, as in "I should be able to run to the top and back to the hotel in maybe 1.5 hours." I had no plan, didn't Google the path, just went straight towards the top, without even following any trails. I wore shorts, a t-shirt and running shoes. No phone. I ended up in a very dangerous side of the mountain full of cacti, it was also very slippery and the rocks had a very frail composition - I tried not to create a rockslide. Once I reached the top HOURS later, I saw elderly tourists up there and thought "how the heck did they get here?!" Then I obviously learned there's a much milder path from the other side of the mountain, which I followed down the mountain. I think I got back maybe 6 or 7 hours later, completely drained. I did ask for some water from other hikers, otherwise a sunstroke would not have been far away. Looking back, I was a complete idiot for not even doing basic Googling before heading up the mountain, not having a hat, not taking water with me, etc.