I stayed at the Hilton once and they even charge their guests a fee for boat transportation to Sunset Key so don't believe they offer day passes to visitors. There is a beach very close that you can go to...it's at Fort Zachary Taylor State Park. Entrance to the Park is through the Truman Annex right near the pier. I recommend a taxi for the short ride to the Park (it's too hot in Key West to walk although I have seen people do this). You can tour the Fort if you like or just hit the beach. You can rent lounge chairs and there are restroom facilities and a snack bar and picnic tables. The beach is protected by rock outcroppings which you can swim out to and snorkel. The water is usually crystal clear. If you have a pair of water shoes, bring them along, the beach has lots of shells and little pebbles. I usually bring my chair to the water's edge. It's a nice beach to get in a little tanning time and the water is beautiful to swim in.