City officials are seeking proposals to remake a downtown Minneapolis block that has served as little more than a parking lot for decades.

The city-owned block north of the Central Library along Nicollet Mall was once home to the Nicollet Hotel, which towered over the city’s now-razed Gateway District. The hotel was demolished in 1991.

In its place, the city will accept nothing shorter than a 20-story building, according to a request for proposals released Wednesday. The layout of the building would also need to accommodate the city’s proposed streetcar line, which would make a turn there from Nicollet Mall to Hennepin Avenue.

“Proposals with a building or buildings at least 20 active floors in height with a mix of commercial, retail, residential, office, and hospitality uses, active street front retail, and preference for substantial integrated public/green space will be deemed responsive to this request for proposals,” the city’s request said.

One potentially controversial component of the plan involves possibly affixing a skyway to the city’s César Pelli-designed Central Library, one of the most celebrated pieces of modern architecture downtown.

The request says all proposals should include concepts that “are designed and constructed to accept a skyway” crossing 3rd Street. Council Member Jacob Frey said this does not necessarily mean a skyway will factor into the final plans, however.

This is not the only proposal to attach skyways to the library. Opus Development Co. is planning to build two towers just east of the library, with the intention that one connect to the building via skyway.

Past efforts at redevelopment of the Nicollet Hotel site have been stymied by an obligation to incorporate an integrated transit terminal on the site, since the city bought the land with federal transit funds. The city managed to have these requirements removed.

“The Nicollet Hotel block is arguably the sexiest parcel in the city, and consequently we will not settle for anything short of iconic,” Frey said in a statement. “In one fell swoop we can add people to downtown, create green space, and trigger connection to the river. Designers and developers better bring their A Games.”

Frey said this also creates a way for a park to be privately funded. “It would be open public space,” he said. “We’d increase the number of eyes on the street in that area, which at times is lacking right now.”

Two options for accommodating the streetcar line — which is still not a certainty — involve either building along a diagonal or leaving some extra space on 3rd Street.