Pioneer Square has plenty of historic hotspitz, as it is Seattle's oldest hood. If you want to learn a bit about the place for free, I'd recommend Milepost 31, which bills itself as the city's most boring exhibit. I didn't think so. Instead, there are a lot of pictures and passages about the people who founded the city and built up Pioneer Square from nothing. There's also bit about Big Bertha, once the world's largest tunneling machine, built in Seattle (most "boring," get it?) It's certainly worth a quick stop since it's free. It made me appreciate Pioneer Square more as I strolled around after my visit.