Ship Islands and Fort Massachusetts, Gulf Islands National Seashore is a 2 mile heavily trafficked loop trail located near Biloxi, MS and is rated as moderate. The trail is primarily used for hiking, walking, sea kayaking, and surfing and is accessible year-round.
My wife and I have been here several times from 2006 through 2014. Take your sunblock! Although I wouldn't recommend going out of your way to make this trip, I do recommend it if you're in the area. Take your sunblock! Insect repellent isn't always necessary but occasionally it is appreciated. There is no shade unless you rent umbrellas from the boat company. The fort is moderately interesting. Watch for dolphins on the boat ride out to the island and occasionally swimming along the beach. The condition of the beach is variable; sometimes it's pristine with fresh white sand, other times it's black and/or covered in washed-up dried-out seaweed. Did I mention to take your sunblock?! On weekends the main beach area can be over-run with people but it isn't hard to walk up the beach far enough to get away from the crowd. You can bring a cooler on the boat ride to the island, highly recommend roller coolers as the walk across the island to the gulf-side beach is long if you're carrying a cooler.
I was here back in 2004 while stationed at Keesler AFB. You have to take a boat out to the island and the walk isn't very far. The boardwalk across the middle of the island is interesting and we could see an alligator in a small pond. The beach on the far side of the island is very nice for walking or surfing. A good hike would be to make a circle of the island.