Learn Swedish: Besökaren tittade på alla salar. - The visitor looked at all the halls.

In Swedish, when alla (all) is used directly in front of a plural noun, that noun usually takes the indefinite plural form. So you say alla salar (literally "all halls") rather than using the definite form salarna, even though we say "all the halls" in English.

How does besökaren (the visitor) get its definite ending?

The word for "a visitor" is en besökare. For en-words that end in -are (which are often people doing an action), you only add an -n to make it definite, rather than an extra -en. So, en besökare becomes besökaren.

Do I always need to use på with tittade?

You need på when you want to say you are looking at something, just like in English. Att titta means "to look", but att titta på means "to look at" or "to watch".

Can I use alla on its own without a noun after it?

Yes! When alla stands alone, it translates to "everyone" or "everybody". For example, if the sentence was just Besökaren tittade på alla, it would mean "The visitor looked at everyone".