Testbeds remain indispensable instruments for experimentally evaluating IoT-oriented low-power wireless networking solutions. With the evolution of the field, they are increasingly expected to match envisioned deployment conditions of such solutions, notably in terms of scale. However, large-scale testbeds are scarce, likely because they have been believed to be expensive. This paper argues that this belief need no longer be justified by presenting the architecture and basic properties of 1KT, our new smart-building IoT testbed for solutions utilizing IEEE 802.15.4 and Bluetooth Low Energy. It comprises 1000 experimental devices deployed directly in human spaces of 168 rooms on all 5 floors of a sizable building. At the same time, its cost is relatively low considering the scale.