Maid of Sker

Once leaving the basement of the hotel ( around half hour into the game ) you'll be outside on a path that leads to a graveyard. Follow the path until you reach an archway with a fire next to it and the cutscene with the dog running through. This is the entrance to the graveyard. Instead of going through go to the left and through the bushes is a large stone whale press to interact with the Whale and get the achievement.

Can confirm that this achievement is NOT MISSABLE and can be achieved once you complete the game.

If you have completed the game already, select Continue from the main menu
From here, go to Ground Floor of the Hotel, and to the far East Church. Return to the secret passage in the Church and descend down the stairs to your left.

From here, you will have no map to guide you. Take a right and follow the passage round. You should see a ladder to your right after walking for a short time. If you reach the save room, simply turn around and walk backwards until you see it. It will be in plain sight.

Climb the ladder and you'll be at a Cemetery, with still no map. Walk in a North-Westerly direction until you see an arch with a flame nearby. Go through the arch, turn around so that you are facing into the Cemetery, and take a left down the edge of the wall. You will come to a large bush but you can walk through this one. Just beyond will be the Whale Sculpture. Interact for the achievement.

After exiting the hotel for the first time, you'll find yourself near a graveyard with a burning fire by the entrance. Ahead is a bush which you can walk through. This will bring you to a large whale statue - press A to unlock the achievement.

I reached this point roughly 30-40 mins into the game.