It is a 10 minute walk from Berlin Hauptbahnhof to te A&O Hostels, but I cannot get info from them as to the exact route to take. Do I use the Europlatz ausgang or WashingtonPlatz ausgang from the Bahnhof? And what exact streets am I able to walk on? On the maps it looks like from Europlatz you can get to Invalidenstrasse, go left, then right onto Lehrterstrasse. But is that possible?
Invalidenstraße is a very busy street and there is a lot of construction work going on. Yet you need to cross it either right at Europaplatz - so that's your preferred exit side of the station building.
So cross Invalidenstraße and walk LEFT towards the MotelOne hotel (which is very visible). You can either turn right into the little park before you actually get to the MotelOne or walk around the MotelOne into Lehrterstraße (turn right).
Thank you so much for the very exact info. I am sure many others will benefit from your directions also, and it takes a load off my back.