Your house doesn't need to multiply in order to earn a return. Your house can provide shelter. That is not money, but is an economic good and can also save you money (if you would otherwise pay rent). This is the primary form of return on the investment for many houses. It is similar for other large capital investments - like industrial robots, washing machines, or automobiles.
The value of money depends on:
- the amount of useful economic activity going on (the actual valuable stuff)
- how much money there is in general
- how quickly the money changes hands (the velocity of the money)
As long as the size and velocity of the money supply changes about as much as the overall economic activity changes, everything is pretty much good. A little more and you will see the money lose value (inflation); a little less and the money will gain value (deflation).
As long as the value of inflation or deflation remains very low, the specifics matter relatively little. Prices (including wages, the price of work) do a good job of adjusting when there is inflation or deflation. The main problem is that people tend to use money as a unit of account, e.g. you owe $100,000 on your mortgage, I have $500 in the bank. Changing the value of those numbers makes it really hard to plan for the future! Imagine if prices and wages fell in half: it would be twice as hard to pay off your mortgage. Or if the bank expected massive inflation in the future: they would want to charge you a lot more interest!
Presently, inflation is the norm because the government entities, who help adjust how much money there will be (through monetary policy - interest rates and the like - ask about it if you're interested), will generally gradually increase the supply of money a little bit more quickly than the economy in general. They may also be worried that outright deflation over the long term will lead to people postponing purchases (to get more for their money later), harming overall economic activity, so they tend to err on the slightly positive side.
The value of money, however, has not really "ordinarily decreased" until the modern era (the 1930s or so). During much of history, a relatively low fixed amount of valuable commodities (gold) served as money. When the economy grew, and the same amount of money represented more economic activity, the money became more valuable, and deflation ensued. This could have the unfortunate effect of deterring investment, because rich jerks with lots of money could see their riches increase just by holding on to those riches instead of doing anything productive with them. And changes in the supply of gold wreaked havoc with the money supply whenever there was some event like a gold rush:
Because precious metals were at the base of the monetary
system, rushes increased the money supply which resulted in inflation.
Soaring gold output from the California and Australia gold rushes is
linked with a thirty percent increase in wholesale prices between 1850
and 1855. Likewise, right at the end of the nineteenth century a surge
in gold production reversed a decades-long deflationary trend and is
often credited with aiding indebted farmers and helping to end the
Populist Party’s strength and its call for a bimetallic (gold and
silver) money standard.
-- The California Gold Rush
Today, there is way too little gold production to represent all the growth in world economic activity - but we don't have a gold standard anymore, so gold is valuable on its own merits, because people want to buy it using money, and its price is free to fluctuate. When it gets more valuable, and people pay more for it, mines will go through more effort to locate, extract and refine it because it will be more profitable. That's how most commodities work.
For more information on these tidbits of history, some in-depth articles on: