The thought of a lounge at this hotel brings mirth to any Melburnian! To answer your question seriously though; there is no lounge.
However the hotel can provide you with a unique room - A Twin Guest Room - Interior - with no windows!
Hmm. The current citigate hotel has no lounge or the new 'refreshed' DT will still have no lounge?
Reading the blurb on the DT melbourne website ("coming soon!") there appears to be any number of 'meeting rooms' 2-3 at least - with every hotel offering a bunch of these, and every second office building trying to hock off their spare space as 'meeting rooms' I'd have thought there would be more value in having a lounge.
The DT in BKK didn't have a lounge but I thought I'd wing it anyway - annoyed me so much in the end I doubt I'll go back there, will try the Hilton directly behind it. I guess there has to be a differentiation in the end, otherwise the DT just becomes another hilton with different livery
Still, I fondly remember the last time I was at DT in KL - gave me a much greater Hilton feeling and service than the actual Hilton KL.
Anyway, having stared at the building for a while in google maps, I can now see the obvious, 'interior rooms' - of course, given the placement of the building and its neighbours this must be the case - interesting to note that the difference in price to another room that presumably has a (non opening) window is about $10. Also, looking up at the top of the building looks like 2 floors with what appears to be a pretty substantial balcony - these will presumably accommodate the "Flinders Street Station View" rooms ... or maybe they are a lounge/deck (or the aforementioned meeting rooms????).
Its a HH rating 6 hotel ... same as HotP, and early asking pricing appears to match that, its certainly not cheap. Given no lounge, limited room types and what this might mean for upgrades for status holders, and the price - though choice is always good, the other existing hiltons are probably more enticing to me.