You know, that makes me think - arrows seem totally obvious to us, but would they be obvious to someone from a completely different culture? <- could be 'go this way'; it could also mean 'avoid as if it's the mouth of a crocodile'.

Well as they said above, to dig that deep the civilization needs a non trivial technology, so I would think any human with an index finger would get it (but the problem remains for those who don't have fingers).