I turned into Grand Central from Vanderbilt Avenue, and went down the steps to the first level, where you take trains like the Twentieth Century. Then I walked down another flight to the second level, where the suburban trains leave from, ducked into an arched doorway heading for the subway --- and got lost. That's easy to do. I've been in and out of Grand Central hundreds of times but I'm always bumping into new doorways and stairs and corridors.
This sentence referred to the man or trains?! I don't get the meaning clearly. If it referred to the man why he got lost if that is easy to do?! as mentioned in the bold sentence.
The context is from the short story named "The Third Level" by Jack Finny.