The Rookery, is an island where dragons migrate to around Snoggletog to lay their eggs. It hasn't been proven that these dragons do not return back to lay more of their eggs.
The warm oasis where dragons flock every winter to welcome their new hatchlings and teach them to fly.
When all the dragons of Berk, along with thousands of other wild dragons, left on the annual holiday Snoggletog to lay their eggs and care for their young until the babies matured enough to take care of themselves.
Geography and Physical Landscapes
The Rookery is a large island with a circular lake in its middle surrounded with pristine golden sand. The lake is encircled with rocky mountains and steep cliffs, and has many hot water pools with underground water in it. Gronckles push their eggs into them to suppress the explosive action the eggs produce when hatching.
According to Hiccup's map, it is South-west of the Isle of Berk