What do the gyroscopes used in commercial aircraft actually look like?
The first gyros were mechanical: A spinning wheel with gimbal mount and driven by air pressure. The picture below shows the innards of one which was used in the Supermarine Spitfire (picture source). The black disk on the right is the instrument background and the arm on top moves the vertical needle sideways in accordance with the turn rate of the aircraft. The white coating on the needle is phosphor to make it glow in the dark.



State of the art is to use a ring laser gyro. This is an optical device which sends a laser beam around a triangular or square track in both directions. Rotations will make the light path shorter in one direction and longer in the opposite direction, so the interference between the two beams shifts the place where the waves cancel each other. This shift is registered and interpreted as a rotation. An alternative design uses optical grade glass fibers for the light path.

The placement is important because flexing of the fuselage will give different results for different mounting positions. To my knowledge, in airliners gyros are mostly part of the avionics suite below the cockpit.

See here for a list of sample applications.



Ring laser gyro assembly with three gyros, one for each spatial axis (picture source).

More modern MEMS sensors are on the advance but mostly to be found in backup systems or on unmanned aircraft. They are much more compact and use less power, but their accuracy is lower than that of ring laser gyros.



Silicon Sensing CRS03 MEMS gyro (picture source).