Eurostat is a great stop for comparable aggregated data about housing in Europe.
One of the main indexes it maintains is the House Price Index 2015-2019, in which 2015 is equals 100.
The data here refers to the price paid when buying a new home or one that was already being used, and the index reflects the changes in the annual average price per country.
Looking at the data, we learnt that the countries where the cost of buying a home increased the most proportionally between 2015 and 2019 are Hungary (from 100 to 167.58), Iceland (148.30) and the Czech Republic (141.90).
The one country where the prices have actually decreased is Italy: from 100 to 98.50.
And the average for the EU-27 is from 100 to 120.14.
See the table, play with some basic visualisations and download the raw data here: https://ec.europa.eu/eurostat/databrowser/view/prc_hpi_a/default/table?lang=en
And see here another version that includes data from 2010 (still with 2015 as "100"): https://appsso.eurostat.ec.europa.eu/nui/show.do?dataset=prc_hpi_a&lang=en