Robert Downey Jr. went all out to celebrate his wife of eight years, Susan Downey's, 40th birthday by throwing her a star-studded weekend-long party at Cavallo Point Lodge in Sausalito, Calif., according to E! News. 

The 48-year-old "Iron Man" actor hosted Justin Theroux, Jason Bateman, Joel Silver, Gwyneth Paltrow, Reese Witherspoon, Jon Favreau, Maya Rudolph, Gwen Stefani and Gavin Rossdale and their families for a fun-filled getaway. 

Guests spent the weekend enjoying the amenities at the resort, getting spa treatments, going on walks and celebrating Susan's birthday. 

"It was a great weekend for Susan, and Robert went all out to make sure she knows how special she is," a source told E! News. "Around 50 of their closest friends came up for the weekend and stayed at the hotel in historic houses. It was a very relaxing weekend and there was a lot of time for people to catch up." 

The event kicked off Saturday night, with a birthday party held in a ballroom of the hotel with dinner, dancing, games and a photo booth. The actor reportedly decorated the space with photos of his wife, purple light and white roses. 

After the party, there was a spectacular fireworks show over the water next to the Golden Gate Bridge. The insider told Us Weekly that both Witherspoon and Paltrow brought their children to the celebration.  

"There were kids running around everywhere, and the whole weekend catered to families," the source said. "They had lot of kids' entertainment and the children were included in all of the events, even the nighttime birthday party. The whole group was very tight and very friendly. There was lots of hugging and reminiscing with old friends." 

Paltrow, who has starred with Downey in all three Iron Man flicks, stayed close to her co-star and his wife.

"Gwyneth was very friendly with Robert and Susan," the source said. "They are very close after the movies and couldn't get enough of each other. They were always talking closely and putting their arms around each other."

Partygoers were served brunch (PHOTOS) on Sunday with food trucks from Hapa SF, Bacon Bacon and a coffee bar. According to the source, the menu included pancakes, breakfast tacos, omelets, burgers and breakfast sandwiches.

Guests all sang happy birthday to Susan before packing up their bags and heading off to the airport. The birthday girl was treated to a special cake made out of maple bacon, chocolate bacon, bacon bits, bacon jam and vanilla cake.

"When it was time to go on Sunday, everyone talked about how much fun they had and that it was too short," the source said. "They wished it could have lasted longer."