Once you sacrifice someone the portal opens, if you sacrifice 3 of them u have 3 attemps to go into the portal. If you fail there is no way of trying again.
I don't seem to see a portal anywhere.
Edit - OK... it populated above the other location list items.
My final attempt didn't load properly — it only showed the torch and not the character, so the dungeon never actually started.
It's a bit annoying that the game is now in a fail state as a result.
I will have to look into that immediatly! Thanks for letting me know.