Vattenfallet låg långt från leden.

Because Swedish usually puts the definite article at the end of the noun.

• ett vattenfall = a waterfall
• vattenfallet = the waterfall

Vattenfall is an ett noun, so its definite singular ending is -et.

The base form is vattenfall.

It is a compound noun:

• vatten = water
• fall = fall

So vattenfall literally means waterfall. In Swedish, compound nouns are written as one word.

Låg is the past tense of ligga.

• ligga = to lie
• ligger = lies / is located
• låg = lay / was located

In Swedish, ligga is often used for things that are in a place horizontally or simply for locations in general, especially with places and landscape features. So Vattenfallet låg långt från leden means the waterfall was located far from the trail.

You sometimes can use vara for location, but ligga is very common and often more natural for places and physical features.

Compare:

• Vattenfallet var långt från leden = understandable, but less idiomatic here
• Vattenfallet låg långt från leden = more natural Swedish

Swedish often prefers specific position/location verbs:

• ligga = lie, be situated
• stå = stand
• sitta = sit

English usually just uses be, but Swedish uses these more often.

Here långt is being used adverbially, meaning far.

Although lång usually means long, the form långt can also mean far in expressions about distance:

• långt från = far from
• Det är långt dit. = It is far there / It is a long way there

So in this sentence, långt is not describing the waterfall itself. It describes the distance.

Från means from.

In långt från leden, it marks the point of reference:

• far from the trail

This is the normal Swedish preposition in this kind of distance expression.

Because leden is the definite singular form of led.

• en led = a trail / route / path
• leden = the trail / the route

Led is an en noun, so its definite singular ending is -en.

Led can mean several related things depending on context, such as:

• trail
• path
• route
• track

In a hiking or outdoor context, leden usually means the trail or the hiking route.

Because Swedish usually attaches the to the end of the noun instead of putting it before the noun.

So:

• the waterfall = vattenfallet
• the trail = leden

English uses a separate article, but Swedish often uses a suffix.

No, this is normal Swedish main-clause word order:

• Vattenfallet = subject
• låg = verb
• långt från leden = adverbial phrase

So it follows the common pattern:

Subject + Verb + Other information

Yes, you could. Långt bort från means far away from and adds a little emphasis.

• långt från leden = far from the trail
• långt bort från leden = far away from the trail

Both are correct, but the original sentence is simpler and very natural.

Låg contains the Swedish vowel å, which is pronounced roughly like the vowel in British English law for many learners, though not exactly the same.

It is spelled with å because that is the normal spelling in this verb form:

• ligga
• ligger
• låg
• legat

This is an irregular verb, so the vowel changes in different forms.