Skogafoss waterfall is beautiful throughout the year, but maybe slightly more beautiful in the Winter. I never saw Skogafoss freeze even in the coldest times, but I did hear massive chunks of ice from the river above smashing into the river below.
I took this winter landscape photo from a ledge about two thirds up the waterfall. It is quite a climb with winter clothes and camera gear. The ledge has a shear drop to the bottom of the waterfall, so every move on this icy ledge has to be very careful.