on she went
On she went, past the Mountain Market with its green awning and smells of pipe tobacco and lard from the deep fryer, past the Garden Walk Inn with its.......

Question 1:
How to explain "on she went" from the grammar point of view? I never saw a sentence structure like this.

Question 2:
Is the "past" a preposition or the past tense of the verb "pass" ?

Thank you!

Question

on she went
On she went, past the Mountain Market with its green awning and smells of pipe tobacco and lard from the deep fryer, past the Garden Walk Inn with its.......

Question 1: 
How to explain "on she went" from the grammar point of view? I never saw a sentence structure like this.

Question 2:
Is the "past" a preposition or the past tense of the verb "pass" ?

Thank you!

Answer

1) It's the same as "She went on". "On" is moved to the front of the sentence to make it sound more poetic.
2) "Past" can be a preposition (e.g. "We walked past the building") or a noun (e.g. "In the past, people believed that..."). The past tense of "pass" is "passed". "Passed" and "past" have the exact same pronunciation though, so don't be surprised if a native speaker mixes them up accidentally.