If Emanuel Vigeland was alive today, I'm pretty sure he'd be directing horror films or building haunted houses. His museum/mausoleum is a meticulously-designed installation to create a unique multi-sensory experience. From the lighting to the acoustics to being forced to stoop through the low doorways (check out the Wikipedia entry for an interesting explanation on that), everything seems carefully planned.
When you first enter the room, you can see almost nothing of the art except a few spotlighted areas of the walls. The longer you stay, the more you can see. So unlike a typical museum where you look at something and move on, you keep returning to the same paintings over and over as you begin to make out more and more of the artwork around them. Meanwhile the acoustics in the room force you to move quietly, and the low whispers of other visitors and even the rustling of clothing echoes loud enough to form an eerie soundtrack to accompany the macabre artwork.
It does require some dedication to visit: Limited Sunday-only opening hours, out-of-the-way location, and cash-only admission charge. But it's definitely worth it!
(Take the 46 bus from Majorstuen to Grimlundsveien or walk down from the Slemdal T-bane station.)
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