My job involves a lot of integration work so I'm probably biased, but I find successfully cracking open a poorly documented API and extracting all the data in a

My job involves a lot of integration work so I'm probably biased, but I find successfully cracking open a poorly documented API and extracting all the data in a usable way to be deeply satisfying, especially if you can be confident enough in your edge cases that you think it'll run until the next unannounced and undocumented change comes along.