In reply to KP:
Not sure of why you got dislikes either. People are weird.
So first thing is can you not go climbing on your travels? A month away in Spain or France could be great opportunity.
Assuming that's not possible though the one word answer would be calisthenics. Calisthenics is body weight training with minimal equipment. You can do pull ups, rows or dips on playground equipment or even from a tree branch. There are loads of exercises you can do on the floor - like push ups, planks, hollow body, squats, yoga postures etc. There is a ton of stuff on Calisthenics on Youtube from doing your first pull up to high level gymnastic strength training. If you were committed enough you could come back stronger than when you left.
The only thing you'd be missing would be training for finger strength. You could get or make a small finger board than could be hung from a bar or a tree branch. Maybe not worth it for one month but if you going away regularly it'd be worth sorting out.
You could also get some Monkii bars - super light sling trainer designed for traveling...
https://monkii.co/