Everest Base Camp Trek has been listed as number one trekking trail by National Geographic. The trek takes you to the base of Mt. Everest (8848m), the worlds highest peak as well as to the top of Kalapatthar (5545m). The trail passes through the Namche Bazaar, the capital of Khumbu region and a cultural center of Sherpa people. You will have plenty of opportunities to learn Sherpa culture and appreciate their hospitality. Also, dont miss to visit the famous Tengboche Monastery, one of the biggest monasteries in the Everest region and a perfect viewpoint to watch the splendid and up close view of Ama Dablam (6812m). Trek to Kalapathar will be the most rewarding ever as it offer the best glimpse of Everest not from anywhere in the world. You will enjoy spectacular views of the highest mountains in the world including Mt. Everest, Mt. Lhotse (8516m), Mt. Cho Oyu (8201m), Mt. Nuptse (7861m) etc. The trek entirely takes place through the Sagarmatha National Park area, which is listed as UNESCO World Heritage Site, which is home to such endangered animals as Snow Leopard, Red Panda and Himalayan Tahr.
Short itinerary: 

Day 01: Arrival in Kathmandu airport (1345meters).
Day 02: Sightseeing around Kathmandu valley.
Day 03: Fly to Lukla (2804 meters) trek to Phakding (2610 meters) 3 hours.
Day 04: Phakding - Namche Bazaar (3441 meters) 5.30 hours.
Day 05: Rest for acclimatization at Naamche
Day 06: Naamche - Tengboche Monastery (3860 meters) 5 hours.
Day 07: Tengboche to Dingboche (4410m, 6/7 hrs.).
Day 08: Acclimatization day.
Day 09: Dingboche trek to Lobuche (4930m) 5 hours
Day 10: Lobuche to Gorakshep - trekking to Everest Base Camp (5357) and back to Gorakshep 6-7 hours
Day 11: Gorakhshep to Kalapathar (5545m) and Pheriche (4240m 5/6 hrs.).
Day 12: Pheriche to Namche Bazaar (3440m, 7 hrs.).
Day 13: Namche Bazaar trek to Lukla (2810m) 6-7 hours
Day 14: Morning flight back to Kathmandu.
Day 15: Sightseeing in Patan Bhaktapur and Patan City.
Day 16: Fly back Home