The behaves like the English "into".

In Hungarian one must be a little more exact with one's movements.  Whereas we woudl say that we go to the post office, or go to a party, to the Hungarians this would mean that we stood just outside the building, and didn't step inside.
Rather, we must say that we go into a party, or into the post office.
This is actually far more logical.

When visiting cities other than those in Hungary, we do not go to London, we go into London.

This is the movement towards member of the triad. 

	Tett könyvet az szekrénybe. He put a book into the cupboard.
	Aztán a könyv az szekrényben volt. Then the book was in the cupboard.
	Azután, vitt könyvet az szekrényből. After that, he took a book out of the cupboard.

Generally, flat surfaces use this triad: table, street, face, etc.

Most Hungarian cities and Hungary itself use this case:

• Budapestre megyek. I am going to Budapest.
• Budapesten vagyok. I am in Budapest.
• Budapestről jövök. I am coming from Budapest.
• Magyarországról vagyok. I am from Hungary (i.e. I am Hungarian).

Essentially any three dimensional object that has an inside, such as a box or waldrobe, uses this triad.

When stating how much something costs using a currency, we place the name of that currency into the illative case. It's as if we are asking, "how much, in dollars, does this cost?", but rather than use "in" we use "into."

When asking how much something costs using mennyi how much, we place that question word into the illative case too.

• mennyibe kerül? how much does it cost?
• szaz dollarba kerül it costs one hundred dollars
• szaz forintba kerül it costs one hundred forints