Sabine Pass Battleground State Historic Site — Port Arthur, Texas
This is a free little park with monuments, walking paths, and picnic tables that I discovered quite by accident as friends and I were driving to a wildlife refuge in the area. This state park was a primary Texas port during several wars and is just twelve miles from Sea Rim State Campground (see review here).
When you gaze out over the water, you can actually see the Louisiana border on the other side. The munitions bunkers are still there and there is an interpretive pavilion. A lot of history happened here and you can read more about that on the Texas Historical Commission web page.