Is this as far as I can go ??? The golden child has opened the cave and it seems as though there is nothing left for my poor villagers to do but keep on procreating......

After all the puzzles are complete, the only things you can do is either keep the village going or start over. There will be other events that pop up from time to time, and disasters can still happen to your tribe, but there are no additional challenges.

Actually, many people (myself included) have found ways to make the game challenging and fun for a very long time. It's really a sandbox, open-ended game that allows you to play in ways beyond simply completing the puzzles/milestones. You can find some discussion of what people are doing in these posts:

Look here
and here
and here
and here!