I work on the computer, so my legs over the years have become quite skinny.
I'd like to build them, but I'm travelling full time, so no gym, and I have some injuries.
Two fused vertebrae in my neck, and two near the base of my spine.
My knees are also susceptible to injury, with fluid build up behind one of them.
So with a combination of bad knees, back and neck, how can I build my legs?
Ideally I'd like to get them quite strong. I've used an incline leg press in the past and loved it, but as I'm travelling, can't get access to that kind of gear.
With a significant injury history, you should really ask a physical therapist. It can be as simple as saying "Here's my medical record, what do you think about me starting a bodyweight squat progression?"
I would ask your medical specialist whether Swimming is okay to do with your medical history. While travelling you can purchase tickets to public swimming pools (granted, depends a bit on where in the world you are travelling).
Anyway, I would not take advice from strangers on the internet without a 1:1 consultation with a medical doctor on what is okay to do and what not.
If the leg press was good for you, then squats seem like a good option. Here's a good place to start with lots of options for progression from whatever level you are starting from.