It's a city-wide game of Sardines, reverse hide-and-go-seek at urban scale. One location is hidden; everyone seeks it. When you find it, you join the party already in progress, packing in tighter and tighter until the last seekers arrive.
Ticket holders (free registration required due to venue capacity and the need to send clues) receive text message hints that grow more specific over the course of the evening. The final clue is revealed via RFID tags hidden around the city (scan one, get the location). Tags are distributed citywide so no participant is ever far from one.
The destination is a sea-themed all ages party: thematic music, food, drink, and appropriately-themed attire required for entry. But the party is almost secondary to the journey. Strangers move through neighborhoods they might not visit, scan hidden tags, sift through text clues, and converge on a secret.