I started by looking through my Preschool board and making a short list of activities and pojects that we could do. I tried to keep them limited to simple ideas that made use of items we already had on hand.
The idea is from Imperfect Homemaker's list of 15 (more) Independent Activities for One-Year-Olds. I used painters tape to attach paper towel tubes to the side of the cupboards, making sure that they lined up to make a clear pathway. The girls could put pom poms through the tunnels and watch them come out the bottom. Sometimes we let had them fall to the floor and sometimes we had something under to catch them.
While this was aimed toward the younger crowd, both girls enjoyed playing with the tunnels together.