One of the most memorable spa experiences I've ever had: the King's Chamber in Marienbad, Czech Republic. I'm sure prices have gone up since my bubbly soak, but it's well worth the splurge. I wrote about it in Arthur Frommer's Budget Travel:
"Today I am king--for 40 minutes, anyway, soaking under frescoed ceilings in the very tub that once held England's Edward VII. Gas bubbles dance in the warm spring water, soothing my skin (and, I'm told, lowering my blood pressure) as I doze off, happy as a clam: this regal indulgence, this rococo chamber worthy of a museum, is mine for all of 20 bucks. Welcome to Marienbad (Marianske Lazne in the tongue-twisting local language), one of three-dozen Czech spa towns where a day of Old World pampering, medical treatments, and three hearty meals can cost as little as 1,750 Czech crowns ($50) per person per day in low season (generally October through April)--less than a standard hotel room in most of western Europe (in high season, prices run from $71 to $95, still a decent deal if you don't mind the crowds).