There is a tablet here - and a very non-puzzly note addressed to Indy. It reads:

Indiana!

These ancient civilizations build the most ridiculous places, don't they? Seriously, it's not that hard to go around it.

Anyway, look, some bank hired me to get a tablet, but... a bank, really? This is more your bag, so I took the tablet and left you that clue to follow me. Here you go - I hope you know what to do with it.

Sorry about the snakes.

Nathan Drake

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After examining the tablet, Indy tells you:

This tablet seems to be some sort of calendar system. It looks like records - or possibly even predictions - of events. Maybe we can decipher it and find some *real* treasure! I think we need more than one tablet, though.