I found this in the admin menu for tumblr...
Elettra Wiedemann Models Her Dress for the Costume Institute Gala with Designer Prabal Gurung
Read more about Elettra’s dress (originally made for her grandmother, Ingrid Bergman) at Vogue.com.
The composition on the photo was interesting to me on first glance, and I thought they were on the prow of a ship (à la Titanic) rather than the top of a building.