It's sunshine, and what's better: it's sunshine that will last. No matter how long it takes them to get outside, they'll get at least fifteen minutes of pure sunshine. It's bright, honestly. Brighter than sunset usually is. And warm? Unnaturally warm for this time of year. But whatever! Are they really going to complain about too much sun?

Maybe they should.

The light will grow brighter and brighter, til it's hard to see. Til it hurts to see, searing, white-hot and overwhelming, but if they try and head back to the museum, they'll find themselves locked out. They have to face the sun, pupils dilating in a desperate attempt to compensate, tears long since burned away, blinded--

--and sooner or later, that's how the dream ends. With the memory of the sun on their skin, overwhelming them.