Santa Elena and Flores are sister cities deep in El Petén; unlike the highlands, being around sea level means these two cities do not have the bone-chilling freeze of the South. Santa Elena is a typical Guatemalan town (except slower moving), and Flores is a tiny island in the Lago Peten Itza connected to Santa Elena with functions as a tourist hub. The town itself is beautiful; think of it as the Antigua of the North. Tuks-tuks cost 5Q each, although the towns are small enough to walk in.
Tikal, a 1 ¼ hour drive away, is the regional highlight. It was an old Mayan capital, and it features impressive ruins and temples deep within the jungle. Be sure to bring water and snacks for the 10km walks! Although the temples and complexes are all intriguing, I would recommend skipping the Temple of the Inscriptions (Temple VI) if you do not have the time; the jungle walk there is possibly more interesting than the inscription-less ruin. Also, watch out when climbing Temple II and V; one slip equals death sacrificial-style... Finally, bring extra money as the ticket price jumped to 150Q as of Feb 2009. If you like Tikal’s partially excavated temples, consider a hike to El Mirador; someone I met there was able to do a 8-day jungle hike with food and camping equipment for $200 out of Carmelita.
To get to Tikal from Flores/Santa Elena, you can take a minibus which leaves on the hour through San Juan Travel Agency in Flores (60Q r/t as of Feb 2009), or take regular microbuses which go around town looking for passengers. If you go the microbus method, (from experience) I would strongly recommend not buying the round-trip; the driver has no incentive to return to pick you up and will demand cash up-front. Beware of the fleecing $10 USD microbuses that meet the buses! If you get stuck in Tikal, you can probably get on a random bus for 30Q. One can reasonably see the place in 6 hours.
One doesn't just find engrish in China...
Templo I, Tikal
Flores from my hotel