From the Super Mario Wiki
Bowser Path is a road which leads to Bowser's Castle in Mario & Luigi: Bowser's Inside Story. It can be accessed by traveling northeast of Bumpsy Plains. The area contains many conveyor belts and requires the use of the Sliding Punch. Bowser saved his Shy Guy minions on Bowser Path and learned the Special Attack Shy Guy Squad. There are 10 Beans that can be unearthed on Bowser Path. The road ends in Bowser's treasure vault, located under his castle, which is where Bowser encounters the Fawful Express.
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