How does an advertising entrepreneur spend the fortune he’s amassed by the age of 40? Purchase a yacht, or perhaps even a tropical island?

Not Christian Boros. He bought a World War II bomb shelter in Berlin with 6-foot-thick concrete walls and clanking metal doors. He then spent five years converting it into an exhibition center for his Contemporary art collection and a home for his family.

“The reason I bought it was not because I wanted a bunker, but because I wanted somewhere to put my art,” Mr. Boros, now 43, said by telephone from Wuppertal, which is near Düsseldorf, where his Boros Group company is based. “I did provoke people at the beginning, but now it’s done, lots of people are happy that such a spooky World War II building has been newly interpreted with Contemporary art.”

The aboveground bomb shelter was built in 1942 under the direction of Albert Speer, Hitler’s chief architect, and was designed to protect as many as 2,000 rail passengers and local residents from Allied air raids. After Berlin capitulated, the Soviet army used it to hold prisoners of war.

Close to Friedrichstrasse in the center of the old East Berlin, the menacing, 52-foot-high building has no windows, just small slots for ventilation. Its steel-reinforced concrete walls and lack of daylight keep the temperature constant in winter and summer. That made it an ideal location for an East German fruit and vegetable company to store scarce tropical fruits, earning the building the nickname “Banana Bunker.”

After the fall of the Berlin Wall, the shelter became the property of the German government, which left it derelict. At that time, any deserted building in Berlin was a potential party venue, and the bunker hosted techno events as well as S-and-M parties that grew increasingly hard-core. The police attempted to close it down after a 1995 event called “Sexperimenta,” yet failed to prevent “Overtures to Lust” from taking place there the next year.

Mr. Boros bought the bunker in 2003 and renovated it with the help of Jens Casper from the Berlin firm Realarchitektur. The work was demanding: Builders had to use diamond saws to remove the reinforced concrete walls and ceilings between the tiny rooms. At the top is Mr. Boros’s family home — a penthouse with a roof garden, and swimming pool.

“The main difficulty was making 70 rooms out of 120,” Mr. Boros said. “We had the bad luck of dealing with the most solid concrete that exists. There are no windows in the bunker, so all the concrete had to be cut into little pieces and transported downstairs and carried out.”

Very little daylight penetrates, and when the heavy metal front door clangs shut, it feels like you are entering a dungeon. The first artworks reinforce the claustrophobia and evoke death: Kris Martin’s swinging, soundless bronze bell and a metal skull, created using medical X-rays of his own cranium, are displayed in a dark, cell-like room near the entrance.

Yet most of the 70 or so works challenge the oppressiveness of the bunker rather than add to it, playing on themes of light and space. The artists themselves chose the rooms for their works and helped design the display.

Mr. Boros, who has about 500 works in his collection, said one of his favorites is Olafur Eliasson’s magical “Berlin Colour Sphere” (2006), an oversize lamp that refracts the colors of the rainbow in patches, filling a room.

Anselm Reyle’s luminous yellow hay wagon, lit by neon, leaps out of the gloom in one room. A pile of Mr. Reyle’s hay bales, sprayed silver, glints in another. The color lends them a metallic look that dissipates as you enter the room and catch a whiff of the farmyard.

Black cubes by Kitty Kraus let light through slits in the edges. In a dark, confined room, the work creates an interior architecture of lines, angles, and boxes reflected on the walls. Tobias Rehberger’s jungle of brightly colored, illuminated mobiles guides the visitor through one part of the labyrinth.

Companies that use the services of Mr. Boros’s advertising agency include Coca-Cola Co., Toshiba Corp., UBS AG, and General Electric Co. Boros Group also does the advertising for arts institutions, including the Venice Biennale.

The current exhibition will stay for two years. After that, he aims to change the display every year to show other works from his ever-growing collection.

In June, Mr. Boros began tours of the bunker for the public. Initially scheduled only on Saturdays, the tours have proved so popular that they now take place on Sundays, too, with two tours a weekend in English. They are booked up until October, yet Mr. Boros said he doesn’t want to start letting visitors in midweek.

“This isn’t a museum,” he said. “This is a private space, and part of that means it shouldn’t be open every day.”