I work in People Operations (Human Resources) and most of my day is spent at my desk working at a computer (or in meetings with other people). I think the most "fun" part of my job is when I get to use my creativity to solve problems and improve processes. I like to think that there is always a better way to do something, so using my brainpower and experience to come up with new ideas is really fun for me.
For example, I used to be responsible for drafting offer letters for new employees. The recruiters would send me an email with the information for the letter (such as the name, title and compensation), but sometimes the recruiter would forget to include important details that was needed for the letter (such as the work location or the name of the manager). We would email back and forth until I had all the information required. This took a lot of time and I thought there might be a better way. I brainstormed and did some research and ended up creating an online form that had a field for each piece of information I needed for the letter. I asked the recruiters to use the form instead of sending me an email. It instantly helped streamline the offer letter drafting process and I could see the results of my work very quickly (it also freed up some time so I could work on other things I found interesting).