Looking for movie about aliens which was boiling water at noon.


I am looking for a movie that i've seen as a child on TV (so it was from 80s probably).
I don't remember much but plot goes something like this:
A treasure hunter finds some kind of cult city in the desert.
That cult has some sort of ritual at noons (not every noon, there was some sort of astronomical thing with that) - they were all assembling in some sort of building with a pool, waiting for water in that pool to boil, but there never was enough sun.
In the end it turned out that this "cult" was aliens and they were kickstarting their spaceship(s?) using the energy of the sun.

I tried several movie lookup services but found no matches. It might be that I am mixing two movies together, but as I remember that TV channel had a week of, how do you say... "colonial exploration-adventure" movies - so I was able to find "Allan Quatermain and
the Lost City of Gold" movie that was aired that week. I am not sure that many people is familiar with the channel as it is not from english-speaking country and not a big one.

Part of it sounds like the movie SHE. There are two versions. Every so often a flaming pool would turn to green fire and grant immortality if you stepped into it. When the sun or the moon shown on it when things in the universe are in alignment.