Making use of facilities without paying:
It is forbidden to enter a person’s property without their permission. This applies whether the property is owned by a Jew or a gentile. It goes without saying that one may not make use of facilities within another’s property without their permission, such as to use their swimming pool and the like. This applies whether to private property, such as a home, or to property of a business, which is owned by the business owners. [Accordingly, it is forbidden for non-guests to make use of hotel facilities, under the guise of a guest, such as to use the gym, swimming pool, partake in meals, and make use of any other amenity that is restricted only to guests. Likewise, it is forbidden to make use of a Mikveh without paying the due fee. It is forbidden to enter a bus or subway without paying the fare, and so on and so forth of all cases of the like.]
 There are several sources which back this prohibition: 1) So rule regarding a stolen home and seemingly the same would apply to using someone’s property without their permission: Admur Hilchos Gezeila 11 “It is forbidden to enter the home for shade from the sun, or protection from the rain, or to pass through the field”; Michaber C.M. 369:2; Rambam Gezeila 5:3; 2) So rule regarding the rule of Zeh Nehneh Vizeh Lo Chaser that we never force another to let someone else in their property: Rama 363:6 3) So rule regarding stealing with intent to return: Admur Gzeila Ugineiva 3; Michaber C.M. 348/1; Rambam Hilchos Gneiva 1/2; Learned from Braisa Bava Metzia 61b “Liminkat” regarding stealing in order to pay Keifel [See Kuntrus Achron ibid 1] 4) By a private home or area, this is also forbidden due to Hezek Reiya: Admur Nizkei Mamon 11-13; Rama 154/3; Michaber 357/1 “Hezek Reiyah”; Tur 157; Rosh Baba Basra 1; Baba Basra 2b;
The reason: Entering another’s property without permission is prohibited due to stealing and if it is a private area, such as a private home, it is also forbidden due to Hezek Reiya. Vetzaruch Iyun in a case that Hezek Reiyah is not relevant if the prohibition is a Biblical transgression against stealing or not.
Other opinions: Some Poskim rule it is only forbidden to steal with intent to keep the item, however to steal temporarily is permitted, and so is done on a daily occurrence. [second Pirush, and conclusion, in Shita Mekubetzes on Gemara ibid, brought in Pischeiy Teshuvah 348/2 and Ketzos Hachoshen 348/1; See Smeh ibid who seems to learn in Michaber that stealing for pain is to keep the item; Pischeiy Teshuvah 348/2 and Ketzos Hachoshen 348/1 conclude it is proper to be stringent] Seemingly, according to this opinion, the same would apply to entering someone’s property without intent to steal. However, in truth, there are other prohibitions involved here, such as Hezek Reiyah, and using facilities that are meant for payment, which certainly would apply even if one only enters temporarily.
 Admur Hilchos Gezeila 1 and 4; So rule regarding the rule of Zeh Nehneh Vizeh Lo Chaser that we never force another to let someone else in their property: Rama 363:6
 Making use of facilities which are intended to be used by paying customers is considered stealing: See Michaber C.M. 363:6 regarding one who stays in a hotel without paying