Once in the kitchen, open the cabinet under sink. Use the Screwdriver (obtained in the basement) on Screws to open up the Crawlspace. Enter it.
Now the directions to go to get through the maze are:
UP
UP
UP
RIGHT
UP
RIGHT
UP
UP
UP
Then, take the bag that pops up.
To get back out, keep pressing down until you're back into the kitchen and the achievement will come up.