excellent advice, all!
In Vienna it often gets to around 35° and humid(today is 32°) but 40 is just...that...much...hotter! and while I enjoyed a 2-hour walk today in the middle of the day, that is also different than sightseeing for hours.
for underwear, I always pack old underwear and toss it each day (I bring old grocery bags in my luggage, the kind that veggies and fruit come in, as I have found that often there is no liner to the garbage cans in the hotel room and I would hate to have a maid have to touch my cast-offs.
re: foam flipflops, I never thought about that. I have well-worn crocs flipflops and a good pair of simple but chic leather sandals. What does happen here sometimes is that gum melts on the pavement and when you walk you get stuck each step by long minty strings. I hope that people who spit their gum on the sidewalk are visited by bad karma, like hangnails forever.
I never thought about the heat radiating off the pavement. That is something I will seriously consider. Right now I am eating low-carb-ish anyway, but I never thought of the "carb-coma" effect in the heat. Wise words.
Also, I am not overly susceptible to heat exhaustion but DH IS. So I have to keep a sharp eye on him too, because it can happen so fast. Usually we take a few litres of water each with us when we are going anywhere (I always have water in my bag, 24/7 but as I have big bags I usually take the 1.5 litre bottles with me--to work, shopping, year-round. However, I can't believe that I never thought of buying more of the small bottles rather than the huge ones. Gahh!!! thanks for that, Trillie! can't tell you how many times I have tried to perfectly angle huge bottles under tiny faucets!
a question for Meritxell2010, or anyone else who knows--cobblestones. I am used to walking on cobblestones, as Vienna's streets are mixed. Mostly, though, it is regular pavement. But in some cities (Prague, for example) the cobblestones are about 4" square and those KILL my feet after a long day of strolling around. Here the cobbles are bigger and easier to walk on. How is Madrid for that? issue? non-issue? and thanks for the great Toledo tip!
also good to know about the air conditioning--Germans and Austrians have very odd ideas about air (open windows make you sick, air conditioning makes you sick, certain days have "good air" and other days don't, and bad air days make you sick, although I have never once been able to tell the difference, fans blowing near you make you sick (but urinating and spitting on the streets are quite okay, clearly those habits are healthy) So right now the thought of any air-conditioning makes me VERY happy.
and...lastly...what might be a dumb question: does dry heat "feel" the same as humid heat? I know from long experience that humid cold and dry cold are very different beasts, so I would assume that dry heat is easier to manage? or not? or more dangerous because it doesn't feel as hot?