Monolithos is a special place in Greece on the island of Rhodes. It's a big rock that looks like a mountain with an old castle built on top of it.
A long, long time ago, people who lived on the island of Rhodes wanted to protect themselves from bad guys who might try to come and attack them. So they built a big castle on top of Monolithos to keep themselves safe.
The castle was built really strong and has been there for hundreds of years. Even though parts of it are old and broken, you can still see how strong it was.
When you go visit Monolithos, you can climb up stairs and walk around the castle. You can also see a great view of the island of Rhodes and the sea from way up high! It's a really special place that people come from all over the world to see.