It’s hard to imagine today the deal that went down in here.

Stop in. Take a booth. Order a Gritty burger.

The place was founded as the Nitty Gritty in 1968 after serving as a neighborhood bar and grocery store dating back to 1898. It was a shot-and-a-beer kind of joint. No-tipping. Picnic tables for seating.

Shapiro began booking live music. Muddy Waters, B.B. King, Bonnie Raitt and others performed here. Jefferson Airplane appeared unannounced one night and jammed for 4-hours.

Drawn by live music, the longhaired counterculture crowd -- not a small contingent in Madison -- made the Nitty Gritty their unofficial headquarters.

Anti-Vietnam war protests often raged outside its doors.

“Tear gas canisters were rolled in on the barroom floor while barricades burned on Johnson Street,” according to Shapiro.

By the summer of 1970 the Gritty’s regular crowd included four faces not part of the non-violent anti-war movement: Karl and Dwight Armstrong, David Fine, and Leo Burt. The radicals met in the hazy bar to formalize their plot.

The massive blast, created by a mixture of fertilizer and fuel, virtually the same lethal combination used in Oklahoma City in 1995, killed a UW physics researcher, damaged 26 downtown buildings, and shook people from their sleep as far as 30 miles away.

The bombing ended the radical anti-war movement for good, and it sucked the wind out of mainstream protests to Vietnam. One year after Woodstock defined the 1960s, Sterling Hall defined the end.

Author Tom Bates detailed the bomb plot in his 1992 book “Rads.” Chapter 11 of Bates considerable tome is titled Nitty Gritty.

The Armstrong brothers and Fine were apprehended after years on the lam and served prison time. Burt was never found. Karl Armstrong, sentenced in federal court by Judge James Doyle, father of the current Wisconsin governor, was paroled in 1980 with the help of Congressman Robert Kastenmeier. Today Armstrong runs a popular State Street deli called Radical Rye.

“A change in attitudes and entertainment tastes here on the UW campus and throughout the country marked the end of the music era at the Nitty Gritty,” the menu reads. “The Nitty Gritty has taken a number of twists and turns that have allowed it to evolve into the restaurant and bar that exists today.... Madison’s Official Birthday Bar.”

The restaurant offers family-friendly confines known for secret “Gritty sauce” oozing from the burgers. More than 300,000 birthdays have been celebrated. There’s even an “express lane” for quick service.

As the perky birthday song plays incessantly and the hoi polloi smile perpetually from their picture frames, it’s hard, if not impossible, to imagine the deal that went down here the summer of ‘70.