Learn Turkish: Bodruma indik ve gördük ki kapı kilitli. - We went down to the basement and saw that the door was locked.

Here, ki connects the action of seeing (gördük) to the realization of what was seen (kapı kilitli). It works exactly like the English word "that" in "We saw that...". Using ki this way is a very common way to express noticing or discovering something.

The English translation says the door "was" locked, but kilitli doesn't have a past tense ending. Why?

In Turkish, when you use ki after a past tense verb like gördük (we saw), the state you discovered is usually just written in the present tense. Because the main verb already sets the story in the past, Turkish doesn't need to add a past tense ending like -ydi to kilitli.

Does Bodruma refer to the city of Bodrum here?

No, it just means "to the basement". The word bodrum means "basement" or "cellar" in Turkish. If it meant the holiday city of Bodrum, there would be an apostrophe before the suffix for a proper noun: Bodrum'a. It is only capitalized here because it is the first word of the sentence!

How is the word kilitli formed?

It comes from the noun kilit, which means "lock". The -li suffix means "with" or "having". So kilitli literally means "with a lock," which gives us the adjective "locked".