The beautiful stamp franked on the top left corner belongs to the "UPAEP, National Festivals" series, issued on 09.08.2008.
The two $250 denomination stamps were issued on 17.08.2008 to commemorate the International Polar Year. An international Polar Year or IPY is a year or so during which many nations coordinate their Polar expeditions, observations and analyses. The third IPY has ended, having begun in 2007, and continued until 2009.
The three $20 stamps belong to a lovely set of 10 cute stamps, entitled "Professions".
This cover was postmarked on 12 Nov 2011 in Antofagasta, a port city in northern Chile and took 17 days to reach me! Hope that my cover will reach Chile soon!