Many of the locals of this area have at least heard of the "Haunted Bunker" hosted by the Coast Guard in an old gun battery, named Battery Francis L. Guenther at the Cape Disappointment Station. I haven't had the pleasure yet of touring through this bunker near Halloween but I've heard that it's a bunch of scary fun.
There's something about those old gun batteries that really bring out the imagination in people, even when they don't have actors with masks on jumping out of dark corners. I encourage you to explore some of the other batteries that can be found either at Cape Disappointment State Park (formerly Fort Canby) or Fort Columbia State Park. These two forts along with Fort Stevens in Oregon formed a triangle of defense, guarding the mouth of the Columbia River with their large guns.
Some of the old batteries are easier to find than others, so feel free to ask a park ranger or interpreter if you want to find out more about them or their locations. The batteries were either named with a number or for a military hero. As you'll see, some of the guns were in place before the U.S. was involved in the first World War, while some of the others were added for World War II.
Two of the gun batteries, Francis L Guenther (1922-1943) and Elijah O'Flyng (1906-1918) are located on Coast Guard property and I would encourage you to contact them if you want to visit these locations. Battery Harvey Allen (1906-1945) can be found right outside the Lewis and Clark Interpretive Center. This is one of the easiest batteries to visit and a map of the battery's rooms is located near the Gun 1 emplacement.
Battery 247 (1944-1946) can be found by hiking to the top of McKenzie Head. This is a good example of a World War II battery and a military dormitory can be found on the way up. The majority of the support or garrison structures of Fort Canby were removed after the fort was decommissioned in 1947 but the concrete batteries are still holding up quite well considering their environment and lack of use.
Some regard Fort Columbia State Park as one of the best preserved examples of a coastal artillery fort in the whole country. The Fort Columbia Interpretive Center is a great source to get a better understanding of what these forts and batteries were all about. Unfortunately, this museum is currently closed for repairs but I'll let you know when you can enjoy it again. In the meantime there are still several batteries that you can check out while you're there. Battery Jules Ord (1898-1944) had three eight inch disappearing guns and is quite an impressive structure to this day. Battery William Murphy (1900-1944) and Battery Frank Crenshaw (1900-1920) both are found near the edge of the water and are both named for heroes who were killed in the Philippine Islands.
Fort Columbia State Park also includes a battery with two guns in place. These guns were not the originals but were put in place in the early 1990's to give visitors a better understanding of what these forts were like while they were in operation. The doors to Battery 246 (1945-1950) are locked for visitor safety. The two six-inch guns on display are rare, but not quite scary.
If you do plan on exploring any of these batteries I recommend that you bring a flashlight or lantern, invite some friends, and avoid visiting them at night. You'll never know what you'll find.