GTA5 gymnasiums are spread all over Lausanne, Los Santos, Tondi and every corner, so there is no need to unlock them. The specific location of the gym is as follows:
1, Winnipeg Fitness Center: Located in Winnipeg District, Tondi, Lausanne, near the famous Winnipeg sign.
2.Mouswald Gym: Located in the eastern coastal area of Tondi, Lausanne.