BOULDER - Iconic restaurant The Sink is the busiest it has ever been as it gets ready to celebrate 90 years in business Saturday, July 20.

Visits to the pizza and burger joint on University Hill in Boulder at 1165 13th St. have been steadily increasing - in part because of national attention in recent years, said Chris Heinritz, co-owner. President Obama visited in April 2012, and the Food Network featured The Sink in a "Diners, Drive-Ins and Dives" segment in September 2011.

"We have really turned into a tourist destination," Heinritz said. "We always were a tourist destination, but ... now it's some place (visitors) have gotta go when they go to Boulder."

The restaurant's 54 full- and part-time employees serve 2,500 to 3,000 meals per week, Heinritz said. Sales have increased 300 percent in the last 20 years, he said.

The 90th anniversary celebration on Saturday will be marked by a special dinner served at The Sink, followed by music at the nearby Fox Theater, where two bands will play. Tickets are available at The Sink and online at the Fox Theater website, www.foxtheatre.com.

Before The Sink received the more recent TV attention, tourists came to see the place where actor Robert Redford worked as a janitor in 1958. Other visitors most commonly are grown-up University of Colorado students, or their friends and family, Heinritz said. The restaurant opened in 1923 as Summers Sunken Gardens, serving European-style cuisine.

Mark Heinritz and Chris Heinritz have owned the restaurant since 1992, purchasing it from Herb Kauvar, who became its owner in 1958.

Prior to its restaurant days, the building was a fraternity house and then a single-family residence, according to Mark Heinritz.

The restaurant started as a European-style eatery in 1923, called The Sunken Gardens, and had a large sunken fountain dubbed "the sink."

In 1949, a CU graduate, Joe Beimford, bought the restaurant and changed the name to The Sink.

By 1955, Beimford sold it to Floyd Marks who, three years later, sold it to his son-in-law Kauvar.