The districts are Lower Woodward; Campus Martius/Cadillac Square/Monroe; Woodward Avenue; Capitol Park; the Library District; and Grand Circus Park.

Among the improvements expected to streetscapes and parks this summer include a prepared food market, food trucks, kiosks, and lawn games in the Campus Martius area as part of a place-making effort intended to give Detroit area residents many attractions in a high-density area.

Also included in the planned improvements this summer are working fountains, a children's play area, and a dog park in Grand Circus Park; concerts, movies, food trucks and carts, and art displays near Capital Park; and music festivals and afternoon and evening concerts at Paradise Valley.

In addition, Gilbert's vision includes a 1500 block of Woodward that includes unique restaurants, pubs, and bakeries; and a 1200-1400 block of Woodward featuring "core urban shopping," such as home retail, fashion and restaurants.

The former Hudson's building would showcase junior anchor stores in the district.

The Capitol Park District would include night clubs and restaurants to make it "a very prime destination downtown," Gilbert said.

Businesses signed to leases in Gilbert-owned buildings include; RAM Construction; UBER; Avalon Films; TubeMogul; Just Topped; Harmony Point; Lindemann Miller Siderius; Neumann/Smith Architecture; Salon Detroit; and Grand Circus.

Today's announcement comes on news of Gilbert's purchase of yet another downtown building.

Crain's first reported Tuesday that Gilbert is the owner of the Vinton Building, a 1917 Albert Kahn-designed building at 600 Woodward Ave. Gilbert confirmed the purchase today and said he envisions lofts and retail space in that building.

The new purchases bring Rock Ventures' portfolio of Detroit real estate investments to 19 buildings and three parking structures.

Rock Ventures, the umbrella entity for Gilbert's portfolio of companies, investments and real estate, has acquired eight buildings so far during 2013. The deals were brokered by Bedrock Real Estate Services LLC, Rock Ventures' real estate development arm.

Since 2010, Quicken Loans has brought more than 7,000 people to work in downtown Detroit.