What is this meant for??

Gods have needs.  Probably where mortal tricks are brought in. Demigods aren’t gonna make themselves?

I’m not sure given its supposed to be Mount Olympus.  What would gods need with a dock???

Don’t think it’s where Poseiden feeds the Kraken. Could be a market of some sort but dock? appears too high and don’t think shipping goods was a thing then. 

We have yet to explore our own Olympus’ and if yours is like mine, it needs some cleaning and decorating. 

you mean you have not figured that out yet?    That’s the backdoor to the gate.  attack that instead of the towers.