Presently I am in Rochester, NY, USA at the Ninth Rochester Conference on Coherence and Quantum Optics.
The interesting part: This conference happens only every 6 (!) years. So the first conference was 48 years ago!! I have been at a number of them and 6 years mean that you see big progress happening from conference to conference. For example, the first conference was held before the invention of the laser which completely changed the field.
Does anyone know a conference which takes place regularly at even larger cycles?