Идёт дождь, тем не менее я иду в парк.

It is raining; nevertheless, I am going to the park.

Breakdown of Идёт дождь, тем не менее я иду в парк.

• я: I
• в: to
• парк: the park
• дождь: the rain
• идти: to go
• идти: to rain
• тем не менее: nevertheless

Questions & Answers about Идёт дождь, тем не менее я иду в парк.

Why is дождь used as the subject with the verb идёт, and what does идёт дождь literally mean?

In Russian weather expressions like идёт дождь, дождь (“rain”) is the grammatical subject of the impersonal verb идёт (“is going”). Literally it’s “rain is going,” but idiomatically it means “it’s raining.”

What part of speech is тем не менее, and how does it function here?

тем не менее is a conjunctive adverb meaning “nevertheless,” “nonetheless,” or “however.” It introduces a contrast between two clauses—in this case, showing that despite the rain, you’re still going to the park. You can often swap it for однако (“however”) or всё же (“still”).

Why is there a comma before тем не менее, and should there be one after it?

Because тем не менее links two independent clauses, Russian punctuation requires a comma or semicolon before it. In formal writing you also set it off with a comma after it:
• Идёт дождь, тем не менее, я иду в парк.
In less formal contexts the second comma is often dropped:
• Идёт дождь, тем не менее я иду в парк.

Why is the park in the accusative case after в—в парк—instead of another case?

The preposition в takes the accusative case when indicating motion into a place. Since you are going into the park, парк stands in the accusative (here identical in form to the nominative masculine: парк).

Why do we use иду в парк rather than хожу в парк?

Russian distinguishes unidirectional and multidirectional verbs of motion:

• иду (from идти) is unidirectional and describes a one-way action in progress (“I’m going [there] right now”).
• хожу (from ходить) is multidirectional and expresses habitual or repeated movement (“I go” as a habit).
  Here you’re emphasizing the immediate action: I’m on my way to the park.

Could you use a future tense like я пойду в парк instead of я иду в парк, and how would that change the meaning?

Yes.

• я иду в парк is present tense and implies you are currently going or about to go immediately.
• я пойду в парк is perfective future and focuses on the action of setting out later (“I will go to the park”).
  The main difference is иду can also imply a near-future plan or immediate intention, whereas пойду clearly places the action solidly in the future.

Could тем не менее appear at the very beginning of the sentence?

Absolutely. You could write:
• Тем не менее, идёт дождь, я иду в парк.
or rearrange more naturally:
• Тем не менее, я иду в парк, хотя идёт дождь.
Starting with тем не менее shifts the emphasis onto the contrast before mentioning either clause.