O.K., not exactly "secret." But these 10 spots around the Hub are either out of the way (leap to Deer Island!) or unusual (a FedEx lot?) or little-thought-of (a sandy beach just off the Red Line). They all offer mini-staycations this summer—whenever that might arrive—whether for yourself alone; yourself and your pet; or yourself and a loved one who's really into waste-water treatment (told ya they were little-thought-of).