The private pilot and flight instructor were performing a cross-country instrument flight rules training flight at night, and while enroute, diverted from their planned destination to a non-towered airport to refuel. After landing at the diversion airport, the pilot attempted to navigate via taxiways toward the ramp environment. As the taxi progressed toward the ramp, the blue taxiway edge lights ended, and a “significant glare” from the hangar lights directly ahead obscured the pilot’s forward view through the dirty windscreen. Believing that they had entered the ramp area, the pilot turned toward the fueling area, but the airplane then departed the paved surface onto grass and slid into a ditch. The airplane sustained substantial damage to the left wing and horizontal stabilizer. The pilot stated that there were no preimpact anomalies or malfunctions affecting the airplane’s operation. Had the pilot and flight instructor elected to discontinue taxiing the airplane after losing sight of the ground ahead due to the darkness and glare, it is likely that the accident would not have occurred.