The workplace is not subject to one place. It is anywhere that is in need of your Services. Most likely you will be working in poor conditions usually after war, famine, disease, and natural disasters, with people in very poor condition.
There is also the choice to work with those in need, in your area. That involves little traveling, but the same type of work. If you want to offer your help to those all over the world, you will be traveling much more frequent.
If you work for a specific organization, that has people in need come to them, you will be working in that organizations building. Your work place is specific to what they want to give.
For example, if you work in a homeless shelter, you most likely will be working all over the building. There are also Business area's of the organization that you can work in. They take care of any kind of paperwork or financial things that organization needs to help promote the welfare of those they help.
Expect work to very. Work will always be available, because there will always be people in need of your services.
It can require long nights, and early mornings dedicated to those in need.