I have no root cellar. Just a 1BR condo on the second floor of a 3-story building. One night a couple years back they forecast possible tornadoes overnight. The only "interior room without windows" that I have is my bedroom closet, so I put my bike helmet, some pillows, my down quilt, several flashlights and a radio in there. Happily I had no need to duck and cover.

My other option would be to run screaming into the building hallway and hope one of my downstairs neighbors is home and lets me into their basement...