 Algorithms and Data Structures,
 Algorithms and Probability
 Complexity and Computability
On the MS program, the following list of elective courses highlight different aspects of algorithms, listing the courses very roughly from the more theoretical (prooforiented) to the more applied (implementationoriented):
 Cryptology (Joan Boyar)
 Combinatorial Optimization (Jørgen BangJensen)
 Online Algorithms (Joan Boyar)
 String Algorithms (Rolf Fagerberg)
 Advanced Data Structures (Kim S. Larsen)
 Approximation Algorithms (Lene Favrholdt) [or Heuristics and Approximation Algorithms]
 Computational Geometry (Kim S. Larsen)
 Network Programming (Jørgen BangJensen)
 Algorithms in Cheminformatics (Daniel Merkle)
 Parallel Computing (Daniel Merkle)
VisuAlgo visualizes many of the structures we work with in the area of algorithms.
Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, Clifford Stein.
Introduction to Algorithms, 3rd ed.
The MIT Press, 2009.
You can of course also talk to faculty members and Ph.D. students, working on topics you are particularly interested in.
You can also attend colloquia and research seminars. It varies a lot over the year how many are scheduled, and you should be warned that most of these are talks from researcher to researchers, so they are hard to follow, but it is fine to try to show up. They usually last 4560 minutes.
You can see scheduled colloquia and sign up for automatic reminders.
A few surveys have been written by group members, giving overviews of a particular area. You should be warned that this is not popular science communication, but research communicated to other researchers, so it can be difficult to read.
 Online Algorithms with Advice: A Survey.
 Joan Boyar, Lene M. Favrholdt, Christian Kudahl, Kim S. Larsen, and Jesper W. Mikkelsen.
ACM Computing Surveys, 50(2):134, 2017. Article No. 19
 Relative WorstOrder Analysis: A Survey.
 Joan Boyar, Lene M. Favrholdt, Kim S. Larsen.
In Adventures Between Lower Bounds and Higher Altitudes  Essays Dedicated to Juraj Hromkovič on the Occasion of His 60th Birthday, volume 11011 of Lecture Notes in Computer Science, pages 216230. Springer, 2018.
You can also consider this list of fairly recent MS dissertation titles (and advisors), which displays quite a variety in topics, as well as in direction with regards to theory or practice.
 2018

 Algorithmic Synthesis Planning (Daniel Merkle)
 Computational Synthesis Planning Using Big Data (Daniel Merkle)
 Generic Approaches for Group Contribution Methods (Daniel Merkle, Marc Hellmuth)
 Graph Transformation, Atom Tracing, and Isotope Labelling (Daniel Merkle)
 Online Problems with Orthogonal Resource Constraints (Kim Skak Larsen)
 2017

 Artificial Intelligence in Action RealTime Strategy Games (Rolf Fagerberg, Marco Chiarandini)
 Contributions to Flight Route Optimization (Marco Chiarandini, Kim Skak Larsen)
 Designing Data Structures with Relaxed Balance (Kim Skak Larsen)
 Dynamic Simulation on Hypergraphs (Daniel Merkle)
 Fixed Parameter Tractable Problems for Digraphs (Jørgen BangJensen)
 Graph Interdiction Problems (Jørgen BangJensen)
 Network Interdiction (Jørgen BangJensen)
 Query Complexity for Variations of Geometric Problems (Kim Skak Larsen)
 Symbolic Methods for Counting Molecules (Daniel Merkle)
 The Entropy Compression Method (Jørgen BangJensen)
 2016

 A Permutation Group Approach to Creation of SelfAssembling Polyhedra from SingleChain Polypeptides (Daniel Merkle, Wojciech Szymanski)
 Carbon Tracing in Chemical Reaction Networks (Daniel Merkle)
 Query Competitiveness for Problems with Uncertainty (Kim Skak Larsen)
 2015

 Computational Complexity and Cheminformatics (Daniel Merkle, Rolf Fagerberg)
 DNATemplated Computing (Kim Skak Larsen, Daniel Merkle)
 LatticeBased Cryptography (Joan Boyar)
 Online Problems with Buffering (Kim Skak Larsen)
 Parallelization of Search Tree Based Algorithms (Daniel Merkle)
 Threshold Implementations of Small SBoxes (Joan Boyar)
 Vertex Labellings with Unique Labels and Their Use in Graph Algorithms (Jørgen BangJensen)
 2014

 A Computational and Mathematical Approach to Synthesis Planning (Daniel Merkle)
 European Football Placement Problems  Complexities and Exact Solutions (Kim Skak Larsen)
 Graph Rewriting for DNA Computing (Daniel Merkle)
 RealTime Fluid Simulation and Rendering in Games (Rolf Fagerberg)