Is it weird to get an erection in a public sauna?

Rub it out before you go

No, but religious nutters will think it so. Don't worry about it, but if some nutter complains just leave.

Possibly embarrassing, but not weird. As you know males are easily aroused by visual stimuli. Even though the situation as described is not a sensual one in reality, your brain may perceive it as such. Just the fact that you are unclothed can be enough to cause arousal. Be as discreet as the circumstances allow and don't worry about what you can't control. 

That's embarrassing, but pretend that you intended it.  Walk around and say "any of you want have a penis measuring contest?"

Nah - men are visually stimulated, so if you are seeing naked women (which it sounds like you are into) then it's totally normal.

I believe that you need to have good sex and followed, that relaxes and the penis remains still for more time. Don't worry those people they know that the men have erections, and they will see that as something normal, alone you relax yourself and it happened to you.   

not weird at all....................

You're what known as a "pervert".

We don't usually do that in the US--in fact, our mommies have made us scared to be seen naked by others of our own sex.  If I was you, I'd ask a man your age or a bit more what you're supposed to do when that happens.  My GUESS is that you should casually wrap a towel around you so it doesn't look like you're showing off or something. 

You should try to keep it to yourself.