I realize that all of this is common knowledge to pretty much everyone, especially people who happen to live along coasts that are geographically similar to the ones in these photos. However, despite me knowing this, I often still resort to a fairly generic "sandy beach" coastline. What I'm saying is that this isn't meant to be a geography lesson or some great revelation, but perhaps some of these pictures and my comments on them will inspire you and help you envision some interesting locations for your game. Or maybe they will inspire you to take a trip to Nova Scotia, I don't know.
Not All Coasts Are Sandy Beaches
Again, I know this is obvious to just about everyone, but I can't ever remember playing a game where the whole coastline was described as covered in giant rocks and boulders. For the purposes of moving, much less fighting, such a coastline should be considered as very difficult terrain. The rocks are uneven, many are slippery and/or covered in sea grass, and between just about every one of these rocks lies a great place for someone to twist their ankle. All of this is true even without considering the possibility of dealing with crashing waves. If a party was forced to fight creatures that were adapted to fighting in such terrain or that could fly, it could be a real nightmare. I'm imagining dexterity checks to keep your balance if you want to move faster than maybe 5 or 10 feet per round, and some pretty great consequences for critical fumbles.
Not All Rocky Beaches Are Treacherous
This is still far from an idyllic white sand beach, but travelling along a coastline that consists of mainly larger rock slabs is still much easier than travelling along a coastline made up of boulders. Travelling right at the water line could still prove quite precarious, but otherwise a person could make pretty good time travelling through such terrain. I sure wouldn't want my ship to run aground on either of these beaches though.
Not All Sandy Beaches Are Idyllic
Just because a coast is sandy, doesn't mean it is a great place to pitch an umbrella and build a sandcastle. The beach above is mostly sandy, but it is also covered in thick patches of sea grass. This stuff is deceptively slippery, and moving fast through it is just asking to fall flat on your back. Such a beach should be considered difficult terrain for the purposes of fighting, and travel along such a beach could prove to be slow and arduous. Something else worth noting from this picture is that coastal areas are often extremely foggy, often limiting visibility to perhaps 50 feet or less. What a great place for an ambush!
Not All Beaches Are Even There All The Time
This picture was taken at low tide, and this "beach" is mainly just a half mile or so of mud that stretches between this cliff face and the water. At high tide, these mudflats all but disappear as shallow water climbs all the way up to the edge of these cliffs. Some areas like the one above could even fill with enough water to allow a boat to travel quite close to the shore during high tide, only to leave it sitting in a mud puddle at low tide. This could make for a very inconvenient situation if perhaps a party left their boat anchored here for several hours and then found themselves needing to make a hasty retreat. Likewise, finding something buried here would require a bit of timing.
Not All Coastlines Are Flat
In fact, sandy tourist-style beaches are the exception rather than the rule, which is why they are always so crowded. A large portion of coastline exists where mountains meet the sea, as is pictured here in the Cape Breton Highlands. The beaches in this region are narrow and sparse, often quickly terminating in sharp cliffs. Deep harbors are likely few and far between as well, and would thus represent a strategically vital location in such regions. Just finding a place to dock a ship in such a region, especially a large ship, could be quite a hassle. This could make a destination that might look easy to reach deceptively hard to get to if the person looking at the map was unfamiliar with the coastline that was being depicted.
That's all I have for today. Hopefully something here sparked your imagination, and gave you something to think about for your next coastal adventure. Or maybe at the very least you thought some of my vacation pictures looked nice. Either way I hope you enjoyed your visit.