A simple map showing a Germany (in the broader sense of the word) from a world in which Bismarck is assassinated in 1866, which leads to Prussian ambassador in Brussels Hermann Ludwig von Balan to be recalled to Berlin and named new Prussian Minister President. The Austro-Prussian War still takes place, however the Prussian forces are less lucky when it comes to Austria. As a result Prussia looses the German Civil War though the German Confederation is still doomed. Italy however even though it isn't successful on land (like OTL) wins against the Austrian navy (in contrast to OTL).
Central Europe is restructured in the Peace of Metz, leading to Austria (since 1867 Austria-Hungary like OTL) ceding Venetia to Italy (Napoleon III acting similiar to OTL by getting it for Italy) and the North German Federation being founded, led by Prussia. Also the groundworks for the South German Federation were led during this peace conference.
In terms of territorial changes inside Germany:
Prussia looses the Hultschiner Ländchen, formerly part of the partitioned Duchy of Troppau, was ceded to Austria and Hohenzollern was lost to Württemberg.
However Prussia was allowed to keep Schleswig-Holstein, as well as the occupied Kingdom of Hannover and the territories of the Grand Duchy of Hesse (Hesse-Darmstadt) north of the Main (Oberhessen) as well as the territories which formerly were Hesse-Homburg (since early 1866 part of the Grand Duchy). The remainder of the Hesse-Darmstadt was reorganized as the Duchy of Starkenburg under its old ruling dynasty. While Prussia also pushed for the annexiation of Nassau, Frankfurt and Kurhessen they refrained from doing so in exchange for paying no reparations. Last but not least Bavaria gained the exclaves of Saxe-Coburg-Gotha and Saxe-Weimar-Eisenach within their domains.
The King of Hanover, furious about his forced removal, goes into exile in France (like in OTL) but lives quite well thanks to his wealth being returned to him (excluding his palaces etc.) instead of being confiscated by Prussia (OTL it became the "Welfenfond"). He still agitates for a restauration of the kingdom, however the leaders of Europe mostly ignore this.
EDIT: Removed French intervention due to lack of plausibility (aka Prussia would've been ruined).