Anahtar deliği kum saatinin arkasındaydı.

Because in Turkish, many noun+noun combinations are written as two separate words, even when English would use one word.

anahtar deliği is a standard Turkish noun compound:

• anahtar = key
• deliği = its hole / hole-of

So the structure is basically key-hole. Turkish often forms this kind of meaning with a compound where the second noun takes a special ending.

The base word is delik = hole. In the compound anahtar deliği, the second noun takes the 3rd person possessive/compound suffix -(s)ı / -(s)i / -(s)u / -(s)ü.

So:

• delik
  • -i → deliği

Also, final k often softens to ğ before a vowel in Turkish, which is why you get deliği, not deliki.

So this is not a random spelling change; it is a normal sound change plus a normal compound ending.

kum saati means hourglass. Literally, it is sand clock:

• kum = sand
• saati = its clock / clock-of

Then -nin is added to make it genitive: of the hourglass.

So:

• kum saati = hourglass
• kum saatinin = of the hourglass

A very important point for learners: the -i in saati is part of the compound, not the accusative ending here.

Turkish often expresses location with words that are originally nouns, and arka means back or rear.

So:

• arka = back/rear
• arkası = its back/rear
• arkasında = at/on its back, behind it

With kum saatinin, you get:

• kum saatinin arkasında = behind the hourglass

So Turkish is using a structure closer to at the hourglass’s back.

That n is a buffer consonant. Turkish often inserts n between endings to make pronunciation and structure work smoothly.

For example:

• saati
  • -nin → saatinin
• arkası
  • -da → arkasında

This commonly happens after the 3rd person possessive ending.

So the n is grammatical glue, not part of the root word.

-ydı is the past form of the copula, so here it means was.

• arkasında = behind it / at its back
• arkasındaydı = was behind it

The y is just a linking sound because arkasında already ends in a vowel.

You can think of -ydı as a shortened attached form of idi.

Because Turkish often uses a copula rather than a separate full verb in sentences like this.

In the present tense, Turkish often has no visible word for is/are:

• Anahtar deliği kum saatinin arkasında. = The keyhole is behind the hourglass.

In the past tense, the copula appears:

• Anahtar deliği kum saatinin arkasındaydı. = The keyhole was behind the hourglass.

So this is completely normal Turkish structure.

Turkish does not have a definite article like English the.

Whether something is understood as a or the usually depends on:

• context
• word order
• case marking
• whether the thing is already known in the conversation

So anahtar deliği can mean the keyhole if the context already makes it clear which keyhole is meant.

Yes. This is a very normal Turkish sentence.

A simple way to read it is:

• Anahtar deliği = subject/topic
• kum saatinin arkasındaydı = was behind the hourglass

Turkish normally puts the predicate at the end, so the location phrase plus -ydı comes last.

So the sentence order is natural and unremarkable.

Yes, but it is not exactly the same in nuance.

• Anahtar deliği kum saatinin arkasındaydı
  = The keyhole was behind the hourglass.
  This treats the keyhole as the known thing and tells you where it was.

• Kum saatinin arkasında anahtar deliği vardı
  = There was a keyhole behind the hourglass / The hourglass had a keyhole on the back.
  This sounds more like introducing or pointing out the existence of a keyhole there.

So both can work, but they do slightly different jobs.

In modern Turkish, ğ usually does not sound like a hard English g.

In deliği, it often just lengthens or smooths the sound between vowels. So it sounds roughly like:

• de-lee-i
• or sometimes almost de-lee-yi, depending on speaker and rhythm

The key point is: do not pronounce it like deligi with a hard g.