Spill lists 5 wineries in St. Helena that accept walk-ins without a reservation. Walk-ins are welcome at 5 of them. A typical tasting is $68. The winery itself maintains the facts on one of these pages.
Do I need a reservation to visit wineries in St. Helena?
Not at the wineries on this page, which take walk-ins. Many other St. Helena wineries are appointment-only, so if a specific winery isn't listed here, assume you should book ahead.