Things are getting serious really quickly!

Ben Affleck and Lindsay Shookus went house hunting with their realtor yesterday in LA, and the couple were particularly interested in a $20 million modern mansion in the Santa Monica mountains. In fact, they checked out the property for over an hour, and left with real estate brochures and materials. They also looked at two $12 million pads in the Brentwood and Pacific Palisades neighborhoods, but they didn't seem too jazzed on those.

The 14,000 square-foot Santa Monica property boasts 9 bedrooms and 11 bathrooms, which they're going to need once they shack up. There's enough room for the Oscar winner's three children and the SNL producer's daughter from her previous marriage, as well as any babies they decide to have together!

The residence also comes with a home movie theater, an infinity pool and spa, a gym, and a sprawling back yard. Oh, did we mention it's brand new?

This is all part of the pair's long term plan, which was discussed before they left their respective spouses.

A source tells X17:
    "Ben and Lindsay want to get married and have a kid. They also want a stable home life for the children they already have, so they want to put down roots in both LA and NYC. Essentially, they will be bicoastal. When Jen Garner has the kids, Ben will live in the Big Apple with Lindsay and her daughter, and when Lindsay's ex has her daughter, she'll be on the West coast with Ben and his brood. They don't want to bounce around, so they're eager to establish two home bases. The Santa Monica mansion is perfect, because it's still close to Jen's Pacific Palisades place and near the kids' school."

It would seem a little fast for them to be moving in together, but you have to remember they were involved for YEARS before they went public!