The only other island platform on the network was the disused King William Street, which converted to an island platform in 1895, before finally closing in 1900.

Old photos of Euston
 

On 7 Feb, 00:49, Keerde wrote:
Station Plan 6 shows a larger plan which incorporates passageways and
lifts & spiral stairs.

And what's the bit going through the north wall of the platforms - I
didn't think anything was beyond that side?

Old photos of Euston
 

In message , Keerde
writes

Station Plan 1 shows the station at Booking Hall Level.

Ah ... a Parcels Office. Wonderful!
--
Paul Terry

Old photos of Euston
 

On 7 Feb, 17:00, lonelytraveller
wrote:
On 7 Feb, 00:49, Keerde wrote:

Station Plan 6 shows a larger plan which incorporates passageways and
lifts & spiral stairs.

And what's the bit going through the north wall of the platforms - I
didn't think anything was beyond that side?

There is still a section of the southbound station tunnel with a wider
diameter corresponding to where the easternmost passageway comes out.
So the hole where it comes out is recessed. Maybe there was just some
kind of support structure for the bridge. No sign that it actually
went through to the north.

I thought it was said in past discussions that the platform was
extended, so it may actually have been the end of the platform at one
time.