Once, I was strolling in the mountains and +all of a sudden+ I +found myself looking at+ an old ruined goldmine.
Co do "out of the blue" to intuicja podpowiada mi, ze to raczej gdy podmiot nie ma _zadnego_ udzialu w zaistnieniu zjawiska. Moze sie myle.
"to gaze _at_ (/into/etc.)" - wpatrywac sie. Zdanie z "...I found myself gazing at.." tez byloby w miare OK, tylko, ze IMO "gazing" gryzie sie z "suddenly".
I was curious what I could find there, so I went inside inconsiderately.
IMO, przecinek przed "inconsiderately". --Second opinion, please! Anyone?
All of a sudden the roof collapsed and I got stuck.
Przecinek po sudden. Jeslibys korzystal/-a z mojej wczesn. sugestii, wtedy dla odmiany np. "Without any warning,".
Luckily [,] I had a mobile phone, so I +called+ the rescue team, but they said that they were unable to help me *straightaway*, since they didn't have a spare brigade.
"right now" bylo wtedy: takie okoliczniki podlegaja zamianie w "reported speech".
And +so+ I had to wait inside the cold dank goldmine.
After a couple of hours +the help arrived+ and I was saved, but I caught a cold.
A moze by, tak dla efektu, rozbic to tak:
.. was saved. Still, I cought a cold.