Start dating first
Dates open after reaching eight hearts and completing the required heart quests. The Bath Soap only appears at Wheedle’s Stall when the player is currently dating someone.
Buy and use Bath Soap
Purchase Bath Soap for 100,000t, then use the item to unlock the Bathhouse Date. The item cannot be sold or given as a normal gift.
Plan the date photo
The first visit to a date type awards a Photo Card. Current community documentation notes that the weather and time of day affect date photos and that there is no way to retake one, so save and choose your outfit beforehand if the image matters to you.
Primary sources
Checked against these public pages. Official sources define confirmed features and status; community sources are labelled as such and used for game data that the developer does not publish directly.