The 12 year cycles:

 We each experience a unique mixture of planetary transits in a lifetime. The planets travel at their own speed, marking cycles of challenge, crisis and growth in our lives. For instance, the majestic Jupiter returns every 12 years.
Kumbhabhishekam, the auspicious ritual bathing at temples is performed every 12 years to synergize the mystic powers of the deity. The Kumbha is bathed with the sanctified holy waters in the sacrificial pot and the pranic powers trickle down a silver wire to enter the deity installed inside the sanctum. The deity, until then only a granite stone image, then transforms into a living representation of the Lord with beatitude, conferring divine blessings on devotees.

The world renowned Kumbhmela returns every 12 years.

NeelKurinji, the purplish wild flower, after which the Blue Mountains of Nilgiris have been named, blossoms gregariously once in 12 years. The tribals, in fact, used it to calculate their age! As we write this post, Kurinji flowers have bloomed in the hillocks of Chickmagaloor, delighting the tourists of Karnataka as well.

(Pics from Celestial Nectar evenings on eve of Kumbhabishekham at Avinashi and Achangulam)