Capital of the Shilla Kingdom for 1000 years starting in 57 BC, Gyeong Ju is now a museum without walls due to the sheer number of grassy mounds, tombs, temples, rock carvings, palaces, pagodas, and castles. They were powerful enough to conquer neighboring kingdoms Goguryeo and Baekje to make it controller of the whole peninsula.
Covering approximately 1300 sq. kilometers, it is not a simple place to visit! Tumuli Park in central Gyeong Jo is a good place to start, with its grass covered tombs, yeilding fabulous treasures, such as from the open tomb Cheonmachong.
Wolseong Park yeilds the oldest observatory in the region, Cheomseongdae, constructed in the mid 600s AD from an intricate mathematical design with number of stones representing months, days and able to show certain star positions.
16km out of the city is the most famous palace, Bulguksa, a UNESCO recognized structure of beautiful architectural and aesthetic design. Among knarled pine gardens on a series of stone terraces, with impressive stone steps (national treasure 'bridges'), this is a beautiful structure, if quite crowded due to its popularity!
Source: Lonely Planet Korea 7th Edition