Well, so you have sailed to explore the seas, and you seem to be lucky!
You have found an island. It's massive, 32 000 km^2. You really can't imagine what riches such a massive island could contain. Problem is, there's a cliff. Not a cliffhanger, real 50 metres of cliff, almost all around the island standing in your way. There's a part of the island where the cliff might be possibly lower, but there are sharp rocks and treacherous shallows in the way.
The closest civilization is around 300 km, and that's just a small island, which is lying far from commonly used sea routes itself and was only settled about 70 years ago. As for the closest frequently used port, you have to sail for 700 km.
Will this be enough to stop you from exploring the island?
I am trying to make it so that this island remains isolated from exploration and contact from 15th century European level civilization. Problem is, the island is huge. We're talking about 1/3 of the size of Iceland here after all. After some thinking, I decided 50 m cliff surrounding most of the island except for the part where there are there are the most treacherous waters might be enough to force the explorers away. Is that the case? Or is this completely wrong approach to my problem?
Also, to specify, the island's population is (or at least was until very recently) intentionally not leaving to explore.
Here is the map of the island.