We demonstrate submicrometer focusing of isolated attosecond pulses in the extreme ultraviolet region using a custom ellipsoidal mirror. The obtained focal spot sizes were verified using knife-edge measurements with a sharp silicon edge, confirming reproducible dimensions down to 0.46 μm × 0.36 μm (full width at half maximum), demonstrating near-diffraction-limited focusing performance. Focusing a 1.1-GW tabletop isolated attosecond pulse source yields a peak intensity of 3 × 10¹⁵ W/cm², and a realistic pathway toward 10¹⁶ W/cm² is obtained by optimizing the beamline throughput. These results establish a practical route toward attosecond nonlinear optics in both gas and solid phases, driven by intense extreme ultraviolet fields.