Barring the immense pressure and lack of oxygen, I’d like a nice 75 degrees or so
In: Planetary Science
Nowhere but right here on dry land in the open atmosphere, pretty much. The temperature increases very quickly once underground. Maybe within a half mile or so of the surface would be tolerable.
If you were near a [hydrothermal vent](https://en.wikipedia.org/wiki/Hydrothermal_vent), it would probably be just about right. Otherwise, the crust in ocean areas is only a few miles thick and it transitions from freezing to over a thousand degrees Fahrenheit in that short range, so you’d probably only want to be about a mile under the ocean floor.
Just right for what?
Well, the “too hot” mantle sometimes oozes up past the crust (which is also pretty hot further down and less hot near the surface) and makes thermal vents in some of the coldest, darkest spots in the ocean and makes a little oasis of conditions for life.
It’s pretty much impossible to pick a specific depth and say that it’s “just right” since the temperature gradient between the crust and the core isn’t the same at every point. Some places are hotter while some places are colder. For example, near oceanic subduction zones, the part of the crust that is being “subducted” is significantly colder than the surrounding crust. Likewise, there are plenty of places (Hawaii being the prototypical example) of “hot spots” where magma is far closer to the surface than usual meaning it would be a significantly hotter area of the crust.
That said, even when an area is “colder,” that’s only relatively speaking. Even “cold” areas within the crust/core would be extremely hot by our standards. The effects of the surface temperature due to the sun/climate are virtually non-existent once you reach about 20 meters deep in the crust. From there, it’s mostly geothermal and radiation heating that determines the temperature. As a *general* rule, the temperature increases by about 25-30 °C for every kilometer of depth. Again, this isn’t always true, though, and in some places, the temperature can *decrease* as you go deeper.
In short, though, you could probably go about a km on average before the temperature would start to become unbearable for humans. In some places, you might be able to get deeper, while in others, you wouldn’t be able to go even 10 meters without hitting superheated rock.
You don’t need to go very deep underground for it to start getting relatively toasty, only a mile or two, depending on where you are in the world.
[In the deepest goldmine in the world](https://en.m.wikipedia.org/wiki/Mponeng_Gold_Mine) the rock gets up to 66C/150F once you get to the deepest point some 4 kilometres down. Since it’s a working mine, you can obviously even get oxygen there.
The pressure isn’t a problem until it is, I know from first hand experience that the rock closes in fast on any tunnel you drill on it. As in, you can literally measure it with a tape measure and a watch.
The Earth’s “Goldilocks zone” would ironically be above ground, at surface level where we humans thrive. Underground spa’s just not built yet.
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