The Short Answer
What you need depends almost entirely on what type of thermal experience you're visiting. A luxury resort spa provides most things. A wild backcountry spring provides nothing. Most destinations fall somewhere in between — knowing the category of your destination before you pack is the most useful thing you can do.
Universal Essentials
These items are useful regardless of destination type:
- Swimwear (check destination requirements — some onsen are clothing-free, some European pools require specific styles)
- Flip flops or waterproof sandals for changing rooms and paths between pools
- A microfiber towel or two — compact, fast-drying, better than cotton for the environment
- A waterproof bag for wet items on the return journey
- Water bottle — thermal bathing is dehydrating and most natural sites have no vending machines
- Cash — many rural thermal facilities, particularly in central Europe, Japan, and Latin America, are cash-only
For Spa Resorts and Managed Facilities
Resort-style thermal facilities typically provide towels, lockers, and changing room amenities. The main things to plan for are access and timing.
- Booking confirmation (printed or screenshot) — many facilities require timed entry reservations
- A small padlock if you prefer your own locker security (provided lockers often use key systems, but some older facilities use shared areas)
- Payment card or local currency for on-site food and beverages
- Light clothing for the post-bath period — most resort experiences include a cooling-down phase where guests rest in lounges or gardens
- Reading material or headphones for rest periods between pools
For Wild and Natural Springs
Natural springs with no infrastructure require you to be entirely self-sufficient. The experience is often more extraordinary — but the logistics are yours to manage completely.
- Navigation (downloaded offline maps or a printed topo — phone signals are often absent)
- Sufficient drinking water for the hike in, the soak, and the return
- Sun protection — many natural springs are exposed, and you may spend hours there
- Insect repellent at lower-altitude tropical sites
- A changing towel or poncho for privacy if the area is exposed
- Snacks — natural springs rarely have food vendors nearby
- First aid basics and emergency contact information
- Leave-no-trace supplies: a bag for your trash, and no soap or shampoo (they damage the spring ecosystem)
For Japanese Onsen
The onsen experience has its own packing logic. Many things are provided — but in a specific form you should know to expect.
- A small cotton towel (tenugui) for modesty between pools — do not bring it into the water
- No swimwear for traditional communal baths (it is generally not permitted)
- Yukata (light cotton robe) is provided at ryokan; bring comfortable clothing for day trips between baths in onsen towns like Kinosaki or Beppu
- Shower kit — most onsen provide soap and shampoo at washing stations, but personal supplies are permitted
- Insulated water bottle — onsen towns often have high-quality local beverages for post-bath rehydration