* The Main Entrance: The most obvious entrance is the Front Gate, located in the heart of the mountain. It's massive and heavily guarded, making it nearly impossible to penetrate without a key.
* The Secret Entrance: This entrance is crucial to the story and is known as the Secret Passage. It's discovered by Bilbo Baggins and is used to get into the Mountain without alerting the dragon, Smaug. It's a very narrow passage that leads deep into the mountain, ultimately revealing the dragon's hoard.
The twist: The Secret Passage wasn't *intended* to be a secret entrance. It was originally a drainage tunnel constructed by the dwarves to get rid of excess water from the mountain. It's ironic that this mundane tunnel becomes the key to outwitting Smaug and entering the treasure chamber.
So, while the Front Gate serves as the main entrance, the secret passage is a crucial element in Bilbo's quest and ultimately proves to be more important than the main gate.