That was requested way back during the Beta test and Yoshi categorically said "no", and has stood firm with that attitude. So I'm afraid we're not going to see open/public dungeons (1.0 had them, but they were basically just big empty areas of underground nothing, only adding to the big empty areas of above ground nothing that 1.0's zones in general were like, and as ARR's design was guided specifically to avoid 1.0's missteps, public dungeons alas were excised accordingly, and will never be coming back I'm sorry to say).