You've honed your skills in the dank tunnels, crypts, and rooms of dungeons across the world. Your senses are sharp and your reflexes are quick when it comes to dodging traps and finding hidden passages. You gain the following benefits:

• Your walking speed increases by 10 feet when you are underground or within an enclosed structure like a dungeon.
• You have advantage on Wisdom (Perception) and Intelligence (Investigation) checks made to detect the presence of secret doors or hidden compartments in underground or enclosed settings.
• When you are hit by an attack made by a trap, you can use your reaction to reduce the damage by an amount equal to your Dexterity modifier + your character level.
• You can add double your proficiency bonus to checks made to disarm traps if you are already proficient in the thieves' tools. If you are not proficient with thieves' tools, you gain proficiency.

This feat makes you particularly effective when delving into dungeons, navigating through dark tunnels, and avoiding or disarming traps. Your expertise makes you invaluable in such dangerous and confining environments.