Would be fun kid hideout space! Awesome dog kennel under the stairs design idea. If you want an indoor dog house, utilizing the space under the stairs for a cozy, attractive and practical space for dogs is a good idea! I love this design.
Note to self: remember this as an idea for cat friendly living room. Add dark rustic floating shelves on the side and create one long platform across the top. Add invisible floating shelves on adjacent walls for more kitty mobility.