Yesterday a pair of bluebirds visited our birdhouse. Unfortunately, they couldn't fit in the hole as it was sized for a Titmouse or Wren. They tried to get in though but they needed a 1.5 inch hole. Then the male took a bath in the birdbath I built.
Here's a picture of that birdbath. You can see the male bluebird on the right splashing in the bath.
Some building details: I took some old redwood from a backyard table (same as birdhouse) and cut them in 3 pieces. Bolted them to an old oak tree stump. Had a glass bath from an old birdbath bought at Home Depot. Bought some brackets to extend the base and layed the glass on top. It's firmly anchored with some rocks and is fine in storms. Small birds will stand on the rocks too. Lastly I ran a drip line from our drip watering up to the bath. Every week during the watering season I dump the water to avoid mosquitoes.
P.S. I put in an order at Amazon for a bluebird house.