You cross a bridge, and keep an eye out for the path which leads to the ruins.
You manage to find it, not because the path is obvious and well- trodden, but because there is an old stone marker, worn with wind and rain over the years, beside it.
You continue on your way, and just before twilight falls, the tower and part of a wall of a very old castle rises from the trees in front of you.
You are happy to have found your objective, and excited, wondering what the X on your map signifies. Hopefully it is some treasure or other important item.
You set up a camp fire, and then wander about in the gathering gloom, looking at the outside of the ruins.
The tower itself still seems to be in fairly good shape. There is a huge, thick oak door. You try it and find that it does swing open with a loud protesting creak if you tug hard enough. The inside is dark and can wait until daybreak.
None of the rest of the castle is complete anywhere. You walk around the outside. You can still see where the walls were; all of them are at least a foot high still, and the one beside the complete tower is still mostly there. There are stairs which lead up to nowhere, and sections which look as though they might be safe enough to climb up to and explore tomorrow.
You retire for the night.
In the morning, you have your breakfast while you survey the situation more closely.
You decide to explore the ruins of the castle
You decide to explore the tower