Best solution for aging cats .  My cats
Do not feel stable on cat trees .  These boxes SQUARE and large enough  for them to stretch out and feel safe.
My shy cats are now actually part of our family .  Retreating from hiding under bed , they feel totally safe inside the box or sunning on top.
 The boxes are well constructive and decorative.  Fit nicely next to our beds. Easy to move room to room.
I purchased 2.