While experimental work in the context of 5G has gained significant traction over the past few years, the focus has mainly been on testing the features and capabilities of novel designs and architectures using very simple testbed setups. However, with the emergence of network slicing as a key feature of 5G, creating larger scale infrastructures capable of supporting virtualized end-to-end mobile network services is of paramount importance for experimentation. In this work, we describe our experience in building such a prototype cross-domain testbed targeting 5G use cases, by enabling multi-tenancy through the virtualization of the underlying infrastructure. The capabilities of the testbed are demonstrated through the use case of neutral-host indoor small-cell deployments, followed by a discussion on the challenges we faced while building the testbed, which open up new research opportunities in this space. CCS CONCEPTS• Networks → Wireless access points, base stations and infrastructure; Network experimentation; Mobile networks;