Antigua Guatemala Handcraft market is a very nice place to browse and buy local handcraft. Prices are usually not fixed, and there is a lot of competition, so you can figure out what are the correct prices for most things. It is clean and enclosed, so you can be pretty much safe. It closes later that most ruins and sites, so you can leave it until the end of the day.
I can take you more than an hour and a half to walk around the whole market.