Many buildings are floodlit at night, giving you the chance to take photographs that are full of vivid colours created by the mixed artificial lighting.
The best time to shoot is during the crossover period between sunset and nightfall when there’s still colour in the sky but ambient (day) light levels have dropped sufficiently for the artificial lighting to be clearly visible. Also try photographing neon signs outside clubs, bars and tourist attractions. Exposure times will run into many seconds, so you’ll need a sturdy tripod to steady the camera and a remote release to trip the shutter. Start out with your DSLR set to auto white balance (AWB) but also experiment with other WB settings such as tungsten or fluorescent to produce unusual results.