Correction: I would like to add decorative elements to the hallway without making it long and narrow.

You're fighting against mother nature there. You can't make Laurel into Hardy.

I love upper floor hallways for family photos done gallery style all the same frames with just the mats different sizes

I agree you cannot disguise long and narrow. You need to add lighting, an area rug and pictures on the walls. You can add a collage of mirrors in different sizes also. Maybe add a table with beautiful accessories at the end of the hall.