In recent months, Germany’s bond yields have been on a decline. And as of 21 August 2019, for the first time, the government auctioned a 30-Year Bond at 0% interest with a yield of -0.11%. By buying negative-yielding bonds, investors are agreeing to make a loss, given that they hold the bond to maturity. The curve below shows the German government yield curve. For a more detailed view, you can select a maturity or even specific dates you are interested in.
Source: Plotly visualization with Python, Bundesbank, TR