When approaching the Obersalzberg from Berchtesgaden, you turn right from Bergwerkstrasse onto Obersalzbergstrasse, crossing over the river. At that point was the first checkpoint. Surprisingly this little partly wooden hut is still there, and still has "1937" carved on it (the eagle and swastika are long gone). There are seven photos of it on Geoff's web site. Search this page http://www.thirdreichruins.com/bgaden.htm for "exterior security zone". You can see the hut in a Google satellite view here https://email@example.com ... a=!3m1!1e3 (it's the small building in the middle with the green roof).
Proceeding up the hill, you'd travel most of the way to the Berghof before encountering the second guardhouse which I'm told was called Torhaus Teugelsbrunn. Below is a crop of a US Army post-bombing aerial photo which shows where this guardhouse was in relation to the 3rd one, followed by a close-up. The location of this guardhouse meant that Speer's house and studio and the Gutshof were inside the second zone. You'll find some pics of the remains here https://www.bunkerfreunde-muenchen.de/m ... mId=298278.