Learn Hardcore French: Le sentier tourne à gauche, puis à droite près d’un vieux pont. - The trail turns left, then right near an old bridge.

Sentier is masculine, so it takes le. It means a narrow footpath or hiking trail, usually unpaved.
Chemin is a general “way/path,” from a driveway to a small road.
Piste is a track/trail (dirt track, ski slope, runway).
Route is a road (typically paved, for vehicles).

How do I pronounce the whole sentence?

IPA: /lə sɑ̃.tje tuʁn a ɡoʃ, pɥi a dʁwat pʁɛ dœ̃ vjø pɔ̃/ Tips:

Why is it tourne and not se tourne?

Tourner (intransitive) = to turn/bend, which works for roads/paths: Le sentier tourne.
Se tourner is reflexive, “to turn oneself” (a person turns their body). You wouldn’t use it for a path.

Can I say prend à gauche instead of tourne à gauche?

For giving directions to a person: Prenez à gauche is very common.
To describe a road/path’s shape, use tourner: Le sentier tourne à gauche (the path bends/turns).

When do I use à gauche vs à gauche de?

tourner à gauche/à droite = turn left/right (no “de”).
à gauche de + noun = to the left of something: à gauche du pont = to the left of the bridge.

What’s the difference between puis, ensuite, and et puis? Do I need the comma?

puis = then (neutral). ensuite = then/afterwards (slightly more formal or sequential).
et puis = and then (more conversational).
The comma before puis is optional; both … à gauche puis à droite and … à gauche, puis à droite are acceptable.

Why is it près de and not près à? How is proche de different? What about à côté de and auprès de?

The fixed preposition is près de = near.
proche de also means near/close (adjective): Le pont est proche du village. With motion or precise location, près de is more idiomatic.
à côté de = right next to, beside.
auprès de is stylistic/formal and often used with people or institutions: auprès de la mairie (with/at the town hall).

Why is it près d’un and not près du? And what is the d’ doing there?

d’ is just the elision of de before a vowel sound: de + un → d’un (no change in meaning).
près d’un = near an old bridge (unspecified).
près du is de + le contracted, meaning near the old bridge (a specific, known one).

Does près de ever mean “nearly/around” with numbers?

Yes. près de 10 km = nearly/about 10 km. In your sentence, it’s spatial (“near”), not numerical.

Why is it vieux pont and not vieil pont? What are the forms of this adjective?

Use vieil only before a masculine singular noun starting with a vowel or mute h: un vieil arbre, un vieil homme.
pont starts with a consonant, so it’s un vieux pont.
Forms:
- masculine singular: vieux (or vieil before vowel/mute h)
- feminine singular: vieille
- masculine plural: vieux
- feminine plural: vieilles

Why does vieux come before the noun? Could I say un pont vieux?

Many common adjectives (beauty, age, number, goodness, size) come before the noun. vieux (age) is one of them.
un pont vieux is not idiomatic; stick with un vieux pont.

Are there any liaisons I should make here?

No required liaisons. Say vieux pont as [vjø pɔ̃] (no linking).
After puis, don’t add a z-sound; just [pɥi a] for puis à.
The x in vieux only links in the plural before a vowel in some cases (e.g., de vieux amis → [də vjø.z‿ami]), but that’s plural and not your sentence.

Could I say vers la gauche or sur la gauche instead of à gauche?

vers la gauche = toward the left (directional drift, not a turning instruction).
sur la gauche = on the left(-hand side), used to locate something: Le pont est sur la gauche.
For turning, use à gauche/à droite.

Do the accents matter in à and près?

Yes:

à (with accent) is the preposition “to/at.” a (no accent) is “has” (3rd person of avoir).
près (with accent) means near; it’s a homophone of prêt (ready). Spelling distinguishes them.