Odd. I asked for the quest from the cat by the "temple" and the marker showed up on my compass, so, if its not showing, it seems you have a glitch. Which download source did you use? I'm asking, because some of the download links are for the 1.42 version (found out the hard way).
Once I got the quest, I followed the markers on the compass and it led me right to the bloody ground and the corpse with the urn, whereas, when the game decides to bug out, the compass markers don't show and the urn doesn't exist.
After starting from scratch, I found the urn and after talking to the so called temple god, I went into that cave and the fake god attacked me pretty much straight away; there was no need to go through that gate you were referring to, the imposter's on the side you can access, but only AFTER talking to the fake god at the temple. (do NOT try and talk to the cat until after you kill the fake, or the game locks up and if you are unlucky, you'll have to reboot to get around it (though, with the windoze ten setup, you can create a second desktop and have task manager open there, that allows you to shut it down with task manager))