entlang
along
As a postposition (placed after the noun) with the accusative, to describe movement parallel to something long.
Wir sind gestern den ganzen Fluss entlang gewandert.
Yesterday we hiked along the entire river.

along
Loading your saved state.
along
As a postposition (placed after the noun) with the accusative, to describe movement parallel to something long.
Wir sind gestern den ganzen Fluss entlang gewandert.
Yesterday we hiked along the entire river.

The word 'entlang' (along) is a compound of 'ent-' and 'lang' (long). It describes a movement or position that extends over the length of something, in other words parallel to it.
Eine lange Allee führte zum Schloss.
A long avenue led to the castle.
The most common and a special use of 'entlang' (along) is after the noun. In this case, 'entlang' always requires the accusative. This word order is unusual for a preposition in German.
Wir spazierten die Promenade entlang.
We walked along the promenade.
When 'entlang' (along) comes before the noun, it is used like a normal preposition. In modern language, it then usually takes the dative.
Entlang dem Flussufer gibt es einen schönen Radweg.
Along the riverbank there is a beautiful bike path.
Using 'entlang' (along) before the noun with the genitive is also correct, but is considered very formal or literary. It is rare in normal usage.
Entlang des alten Kanals standen prächtige Villen.
Along the old canal stood magnificent villas.
at / on
'an' and 'entlang' can both occur with streets, rivers, or other lines. 'an' says that something is at an edge, boundary, or surface, or moves there. 'entlang' describes movement or a position parallel to something long, for example a street or a river. The words are confused because both can express nearness to a line. 'an' emphasizes the place at the edge, while 'entlang' emphasizes the path in the same direction.

Heute läuft der Verkäufer die Straße entlang zum Supermarkt.
Today the salesperson walks along the street to the supermarket.
Wir haben am Fluss eine kurze Pause gemacht.
We took a short break by the river.