Learn Swedish: Draken bor i berget där hjälten sover. - The dragon lives in the mountain where the hero sleeps.

Because hjälten is a masculine word often referring to a male person, it takes the special masculine definite suffix -e instead of the usual -a. You would say där den modige hjälten sover. Remember that you also need to add the separate word den (the) before the adjective!

Why is 'where' translated as där in this sentence instead of var?

In Swedish, var is strictly a question word used to ask 'Where?' (like Var är draken?). When you are connecting two parts of a sentence to describe a location, you must use där, which usually means 'there'. You can think of this sentence as literally saying: 'The dragon lives in the mountain, there the hero sleeps.'

Both draken and hjälten end in -n, but berget ends in -t. Why?

This is because drake (dragon) and hjälte (hero) are both en-words, so their definite 'the' forms just add an -n at the end. However, berg (mountain) is an ett-word (ett berg). To make an ett-word definite, you add -et or -t, making it berget.