Well, east, anyway. The station building is 150-odd metres east of the
junction of York Road and Euston Road; that junction is very roughly the
eastern end of the Northern line platforms, and the western end of the
Victoria platforms.
No, its the EASTERN end of the victoria line platforms. And its a very
long way east of the Northern line platforms. From west to east its
basically Northern Line Platforms - (Below the) Tube Ticket Hall -
Victoria Line Platforms - Thameslink.

The eastern end of the northern line platforms are almost directly
under the Tube Ticket Hall, and the western end are almost under St
Pancras; the middle is where that silvery round thing is on the
surface behind the hoarding, and the eastern end is WEST of the round
tiled thing by WH Smith (on WH Smith's western side) - the round tiled
thing is where the old Piccadilly lift shafts were, and the round
silvery thing is where the old Northern line lifts were.