captain sian

I've completed the games story and I was aiming to do as much as everything else as I can. There are a couple of grottos I just can't find, where I think they may be I just can't seem to get to... I might just be being stupid but there are a few places on the map that are on higher land or surrounded by rock that I just can't reach... is there something I need to unlock like a new mode of transport or are there other ways of getting to these places?

Any help will be appreciated. Thanks.