Here are some things we do most things have to be parent lead, so it is good exercise for you too. I have a few that can be done on their own or begin with me and then spontaneously become his own activity:
Hide and Go seek, Mums turn, Nello's turn. Then we take turns hiding his Clifford the big red dog around the house and go running around looking for him.
Jumping course- I use computer mouse pads-cheap ones from IKEA and put them down on the floor and jump form pad to pad. Then we jump over things, like small plastic bowls or cushions.
Hopscotch-Use masking tape on the kitchen floor and put numbers in each box and practice jumping/hopping and saying the numbers. I use a big flat rubber plug stopper from our sink and let him throw it on the numbers too.
Balloons-Keep up, kicking, chasing etc...
Beach balls and foam Frisbees-throwing and catching etc...
Bubbles-Gymboree bubbles are the best and great for indoors, not sticky or a mess and safe for furniture. Try to catch bubbles on various body parts, of course tummy and tongue are big hits.(they are non toxic and sweet to taste) I give him plastic cups to try and catch the bubbles or a ladle or a spoon to catch them.
Building Forts-I let him pile couch cushions, pillows, towels etc...and make a fort, knock it down, go in it etc...
Animals-We pretend to be different animals and walk and make the sounds like them.
Follow the leader obstacle course (I'm the leader) Go all over the house up and down objects, crawling under tables etc...
Bed Sheet Tug of War-I let him win and I pretend to go flying forward and always fall down for a good laugh on the bed or something
Gymnastics- Wheelbarrow walks, handstands with feet on the couch and hands on the floor, somersaults etc..all with my help of course.
Stomach Wheel rides-We have a small wooden dolly (type for moving small furniture pieces) that he lays on his stomach and "swims" around the floor pumping with his arms and feet, kwim?
Towel or Blanket rides- I give him a short ride as he sits on a towel or blanket and then I leave him to do it with his stuffed animals all around the floor.
Bath-I let him go "swimming" in the bath and play. I take out his regular toys and bring in things like strainers, ladles, kitchen stuff to play with.
A friend of ours did this, Nello not really a fan, so never bothered. She uses a small inflatable kiddy pool and fills it with those small, soft plastic balls and made a ball pit.