A weekend away with two people I'm attracted to — proper ethical non-monogamy with everyone fully on board. The logistics and communication seem like the challenging part but that's exactly what makes it worth planning properly.
Honestly just really good slow sex with someone I'm deeply emotionally connected to, no distractions, no time pressure. Sounds simple but it's rarer than it should be and I want to experience it properly.
Proper BDSM with someone who really knows what they're doing. I've had vanilla attempts at it but I want the real thing — someone experienced who takes it seriously and does the aftercare properly.
A sex-positive retreat or workshop — not as weird as it sounds. There are legitimate places that run workshops on intimacy, communication and sexuality. It's more about personal growth than anything else.