Many European universities offer a wide range of short-term programmes.
From Scottland to Latvia, from Spain to Turkey.
Possible topics: Introduction to Data Analytics (Maastricht), Photovoltaics (Warsaw), Building Information Modeling in Structural Design (Split), Biomedical Imaging (Zürich), The Complexity of Water-Reuse (Enschede), European Business Challenges (Brussels) etc.
Here is a long list of summer schools on offer. They are sorted by countries and topics.