By confining light in a small cavity, the spontaneous emission rate of an emitter can be controlled via the Purcell effect. However, while Purcell factors as large as similar to 10,000 have been predicted, actual reported values were in the range of about 10-30 only, leaving a huge gap between theory and experiment. Here we report on enhanced 1.54-mu m emission from Er3+ ions placed in a very small metallic cavity. Using a cavity designed to enhance the overall Purcell effect instead of a particular component, and by systematically investigating its photonic properties, we demonstrate an unambiguous Purcell factor that is as high as 170 at room temperature. We also observe >90 times increase in the far-field radiant flux, indicating that as much as 55% of electromagnetic energy that was initially supplied to Er3+ ions in the cavity escape safely into the free space in just one to two optical cycles.