Click here for the article about setting up Metaproperty Dependencies
With Smart filters it is possible to have multiple metaproperty columns under one filter.
But it is also possible to only show one column at first and keep the other hidden. This means that the second metaproperty "Country" is depending on the first metaproperty "Continent". After a value is selected of the first column, the second column automatically shows up.
Let's take the filter Destinations as example. Go to Settings > Account > Smartfilter Management and select the option icon for Destinations.
Go to the first metaproperty (with the name Brands, but in fact the label Continents) and select the depending second metaproperty at Dependency, country in this case.