by Julia Tenney and Rebecca Vessenes
Problem:

The video consists of a series of clips. Each of them features a location on the MIT campus, and either an item or a set of thirteen light-and-dark squares. Each clip also features a camera movement—either left-to-right or downwards.

As it turns out, this is a criss-cross puzzle with video clues. The MIT building number indicates the row or column number in the grid, and the camera movement determines whether the clue is Across or Down. The clips that show thirteen squares indicate the light-and-dark pattern of the rows and columns that don’t have clues along them.

The video clues are provided in alphabetical order. The clips that show thirteen light-and-dark squares are mixed in, indicating where the filled-in letters would fall in the order.

Once the grid is filled in, the letters on the diagonal (indicated by the phrase “marks the spot” in the flavor text) will spell out the phrase AFTER SUNDOWN.

 A T L A T L S T A M E N N I W P A E E T A F F E T A B O W L S S E E W O T S A T I N P O D S U A E S A B N E V A D A G I N G E R O E T C E A R A D I O H E A D E R R D E K C A N O E C A T T R E E R E A H E B Y U L T I M A S A T Y R S

List of video clips:

ImageBuildingDirection
AFAAAOI (column 4)4D
ants1D
AODNATT (column 10)10D
atlatl1A
bowls3A
bra13D
canoe11A
cat tree11A
dream5D
ecru1D
ELEER (column 12)12D
ERRDEK (row 10)10A
ginger7A
iced tea9D
keys13D
life saver3D
LTIAIA (column 6)6D
mew11D
nest13D
net3D
NIWPAEE (row 2)2A
OETCEA (row 8)8A
pawns7D
REAHEBY (row 12)12A
sage Derby11D
satinpods5A
satyrs13A
SEEWOT (row 4)4A
SPGHAS (column 8)8D
stamen1A
taboo9D
TAEAL (column 2)2D
taffeta3A
torch7D
tweeted5D
UAESAB (row 6)6A
ultima13A
Uno1D