introduce a fairly high tax on every second (or at least third, progressively higher with each) property to deter buying up properties to rent
perhaps introduce another tax on properties which have been vacant for X months/years
introduce rent control
perhaps even introduce some form house price control (per square meter, tied to median wage, perhaps)
make the government build some housing
You can debate how well each of these would work, but there are many ways to bring prices down without making it less pleasant to live in those houses. I'm most partial to a progressive property tax, rent control and government housing, myself.