Finally got it with the help of the console!
You need to activate the teleport by 'using' between the two rocks in the water near the club entrance. The teleport itself is on the left side of the main entrance to the club. You need to jump because it's above ground in the corner between the outer wall of the club, the rock, and the rope.
Very useful console commands:
find <text>
Finds a console command that includes <text>.
sv_cheats <0 / 1>
Activates cheat mode. Necessary for many commands.
developer <0 / 1>
Activates developer mode. Necessary for the commands below.
find_ent <text>
Finds an entity (buttons, teleports, triggers, etc) that includes <text>.
ent_text <entity id / entity name / entity class / {nothing}>
Shows information about an entity or multiple entities below it. Text shows through all graphics making the entity easy to locate.
ent_message <entity id / entity name / entity class / {nothing}>
Shows information exchange between entities.
I first enabled cheats and the developer mode. Then I used "find_ent port" which got me four teleport-related entities in the map: two teleport sources and two destinations. Each entity has a unique ID and a class. The sources have the class "trigger_teleport" and the destinations have "info_teleport_destination". Then I used "ent_text trigger_teleport" which enabled the see-through info text below every teleport trigger entity. The teleport was then easy to find. The information had "state: disabled" though. Finally I used "find_ent button" to find the activation button. The teleport needs to be activated every time after it's used. Console for the win!