Giant Castle, Prehistoric hillfort in Popelná, Czech Republic

Giant Castle, also called Obří hrad, is a prehistoric hillfort from the Hallstatt period on a rocky spur of the Valy hill at 940–980 m above sea level near Popelná. Its ramparts, 370 × 80 m in plan, were built of two faced stone walls filled with rubble, 3–4 m wide and 3–5 m high, with a fortified bailey on the south side.

The hillfort dates to the Hallstatt period, roughly the 7th to 5th century BC, and is one of the most important traces of Celtic settlement in Bohemia. Archaeologists found wall remains on the northeast slope of Valy in 1926. Some researchers link the site to gold mining and trade, citing Celtic coins from the 2nd to 1st century BC found here.

The name Giant Castle comes from legends that giants built their castle here from rocks and boulders. One tale tells of a poor tailor thrown into the Losenice by angry giants, who survived and found pure gold under the mud covering the boulder hurled after him.

The ruins are located in open nature and can become muddy during wet weather, so sturdy footwear is advisable. The paths across the hill are not paved throughout, so good footing is helpful when exploring the site.

Almost no objects of daily use were found at Obří hrad, neither after its builders nor its inhabitants, which is why researchers consider it may have served as a sacred space rather than a permanently settled fort. The site's finds are kept in the museum at Kašperské Hory.