If I don't pay a debt, then the creditor takes my goods. Why, then, do Greek creditors not take Greece? Normally, when you don't pay a debt, your creditors take your goods (house, car, etc).

If Greece cannot pay its debt, can its creditors take Greek goods (structures, cities, industries, lands, etc)? Can Germany, or other organizations, become owners of Greece?

Maybe that's a silly question, but for a non-expert it sounds logical.
In general, there are three kinds of debt:


Secured debt, like a mortgage or a repurchase agreement. With a mortgage, for example, the debt is secured by a lien on the home, and if the debtor does not pay, the creditor can seize the home.
Unsecured debt, like a credit card or corporate bond. Governments will generally allow creditors to liquidate many of the assets of an insolvent individual or firm to meet unsecured obligations, subject to (often significant) limits. For individuals, things like retirement accounts and primary residences are often off-limits for debt collection.
Sovereign debt. Sovereigns typically issue debt under their own law, and countries generally don't set up their legal systems in such a way as to allow other countries to take their things. However, when sovereigns issue debt under foreign countries' law, as Greece has done with some UK-law bonds, payouts tend to be higher, and overseas property is in fact occasionally seized. However, seizing the domestic property of a defaulted sovereign is effectively impossible, as one of the benefits of being a sovereign is that you control your own territory— attempting to seize another nation's "structures, cities, industries, lands, etc." (setting aside the fact that most structures, cities, industries, and land in Greece are not owned by the government) is what is known as an act of war.