Budapest packs in an enormous range of things to see and do, from soaking in Ottoman-era thermal baths to exploring one of Europe's largest synagogues. The Castle District on the Buda side and the grand boulevards of Pest could fill several days on their own, and that is before you get to the museums, markets, and parks. Many of the best experiences here cost little or nothing, which makes it easy to fill your days without watching your budget too closely.