The HPC2N Grid portal is a user-centric environment that provides a homogeneous interface to a set of heterogeneous High-Performance Computing (HPC) resources from standard web-browsers. The interface includes support for most everyday activities, such as to submit, manipulate and delete jobs, monitor queues and job status, obtain user-, project-, and resource information, view job output, etc. This contribution reviews the portal functionalities and presents the design and implementation of the underlying system architecture. Some major design considerations, features and limitations are discussed. The portal currently gives access to all major resources at HPC2N, in total comprising over 700 CPUs.