In Reger's letters to Hinrichsen, he specifically adds the location "Grassistraße" or "im Restaurant Hannes beim neuen Gewandhaus". According to Popp & Shigihara 1995, Peters correspondence, p. 472 note 1, it was located at number 26.
However, Mr. Wieland Zumpe and Mr. Albert Pöllath investigated the matter and kindly provided the exact location: Grassistraße 12 / Beethovenstraße 17. From the place of which the picture below (from the site of mr. Wieland Zumpe: www.lipsikon.de/) was taken, the Gewandhaus was on the left-hand.
This was not just a small cafe, but it contained a restaurant with a nice Jugendstil-interior as was the habit in those times. And it was located in a very well-to-do neigbourhood. It was Reger's preferred place for several years to meet his friends, as it was lying very near to the Conservatory and opposite to the Gewandhaus.
In my collection, I have also an old Litho-card with exterior and interioir of the Hannes-Restaurant. The impressive site of Mr. Wieland Zumpe with cards of Leipzig also shows this card:
A photo of the interior of Restaurant Hannes could be added to my Reger-collection in December 2007. This is thus the place were Reger lived the last evening among his friends of old.
The Gewandhaus and the Grassistrasse were hit by several bombs. Restaurant Hannes was destroyed. Presently, the Grassikarree is at the location of the old restaurant.
On the evening of May 10, 1916 Reger was in Restaurant Hannes when he felt his health deteriorate. This was before Karl Straube arrived at 11 PM. Karl Straube brought him into Hotel Hentschel. But what was its location?