Ishigakiyama Ichiyajō Historical Park, Historical park in Hayakawa, Japan.

Ishigakiyama Ichiyajō Historical Park is a park in Hayakawa, Odawara, on the site of Ishigakiyama Castle, which Toyotomi Hideyoshi built as a siege camp during the Odawara campaign. Stone walls and earthworks remain on the hill, and an observation deck overlooks Odawara Castle, the city and Sagami Bay.

The fortress was built in 1590 on the orders of Toyotomi Hideyoshi during the siege of Odawara, and the construction was completed in a matter of weeks. Once the siege ended and the opposing lord surrendered, the site was abandoned and never repurposed.

The name refers to the story that the fortress appeared overnight; in fact it was built earlier and the surrounding trees were cut down so it suddenly came into view. Each October the Ichiyajō Festival is held here. Along the Kanpachi road, signboards introduce the individual commanders who joined Hideyoshi's camp.

The site can be reached from the nearest train station by foot or by bus, and the walk up the hill takes some time. Sturdy footwear is a good idea since some sections of the path are steep and can become slippery after rain.

The park opened to the public in 1990, two years after Odawara city bought the designated historic site in 1988. The grounds were registered as a national historic site under the name "Ishigakiyama" in 1959. Each October the Ichiyajō Festival is held here.