Just a few days ago I read a book called "Convict Conditioning". In essence, it's about bodyweight exersices. You won't need a gym, but you'll need a place to hang from.
Copying a part of a book review:
Convict Conditioning is a book of bodyweight only training. It utilizes six training exercises, each having ten different variations. The six exercises are called "the Big Six", and they are one-arm pushup, one legged squat (pistol squat), one-arm pullup, hanging straight leg raise, stand-to-stand bridge, and one-arm handstand pushup. You don't start with these exercises, but rather easier versions, and they represent the ultimate goal of the workout.
The workout is structured so that each exercise of the Big Six is divided into ten steps, the final step being the exercises listed earlier. As a general rule, the first steps are the easiest and you move gradually to more challenging variations. For example, you start the pushups series with standing pushups against the wall, and progress from there into incline pushups against a table, then kneeling pushpus, and so on until you reach the one-arm pushup.
Copying a part of a book review:
Convict Conditioning is a book of bodyweight only training. It utilizes six training exercises, each having ten different variations. The six exercises are called "the Big Six", and they are one-arm pushup, one legged squat (pistol squat), one-arm pullup, hanging straight leg raise, stand-to-stand bridge, and one-arm handstand pushup. You don't start with these exercises, but rather easier versions, and they represent the ultimate goal of the workout.
The workout is structured so that each exercise of the Big Six is divided into ten steps, the final step being the exercises listed earlier. As a general rule, the first steps are the easiest and you move gradually to more challenging variations. For example, you start the pushups series with standing pushups against the wall, and progress from there into incline pushups against a table, then kneeling pushpus, and so on until you reach the one-arm pushup.
http://www.amazon.com/Convict-Conditioning-Weakness-Survival...
I personally love to lift weights, but for the next year I'll be lifting less and doing bodyweight exercises more as an experiment.