The correct answers are Please let me know when you get to the hotel, Please let me know when you arrive at the hotel, and I will meet you when you walk into the lobby.

The verbs get and arrive are both used to talk about reaching a destination, but they take different prepositions!

• Use get to + destination (get to the hotel).

• Use arrive at + specific building/place (arrive at the hotel). Never say "arrive to"!

• Use into to describe the movement of entering a room or enclosed space (walk into the lobby).