The Sólfar (Sun Voyager) sculpture is something I completely recommend, in Winter the light is just gorgeous, yellow and pink skies cause this whole scene to become the most beautiful spectacle.
The sculpture was made by Jón Gunnar Árnason, an Icelandic artist. It is a representation of a dream boat and is an ode to the sun. It tries to create hope, dreams, progress and freedom. There will be lots of people there trying to get their shots, so mindful when someone is taking a picture and try not to ruin it by hogging the sculpture for a long time.
The view of Mount Esja is just breathtaking and with the city behind you it is beautiful. I urge you to go at sunrise or sunset and enjoy!