Learn Turkish: Şişman dev mağarada uzun süre uyumuş. - The fat giant slept in the cave for a long time.

The ending -muş is the reported or inferential past tense. You use it when you are talking about something you didn't see with your own eyes, like rumors, gossip, or things you realize later. It is also the standard tense for telling fairy tales, myths, and stories in Turkish. Since we are talking about a giant (dev), this is clearly a story, so uyumuş is the perfect choice!

In English, we say 'for a long time.' Where is the word for 'for' in uzun süre?

In Turkish, you usually don't need an extra word to show duration. The phrase uzun süre (literally 'long duration') acts as an adverb all by itself. Just place it before the verb, and it naturally translates to 'for a long time.'

I know zaman means 'time.' Could I say uzun zaman instead of uzun süre?

Yes, you could use uzun zaman, and people would understand you perfectly. However, süre specifically means a 'duration' or 'period.' When talking about how long a continuous action lasted (like sleeping), uzun süre is a very natural and exact choice.

Just to review, why is there a -da at the end of mağara?