On our trip this summer we have an 8 hour lay over in Madrid any ideas on how to pass the time?

Take a taxi to Parque del Buen Retiro and have a stroll and picnic. That's what I did, and it was worth every penny. You could also take in a museum, but I preferred the fresh air and exercise to break up a long journey home.

Sounds like a plan!! You might be interested in the Hop on,hop off bus. 2 routes to choose from and worth the $. I kow for sure there is a pick up @ Puerto del Sol.

There's a bus (Aerobus?) from the airport to the train station. I took it from Barajas and back when I was there in April. As I recall, it's not too far from Retiro Park.

There's a Tourist Information booth at Barajas. You can easily and inexpensively take a train into Madrid. You can follow your interests. The tourist bus will give you a good overview of the main sights. If you choose to visit a museum, I'd go to the Thyssen-Bornemisza which is not far from the Buen Retiro park.

from T4 there is a fast train to Recoletos or Atocha.
Both stops give you a number of options to visit the
center and many attractions.
Madrid is hot in the summer!