A physicist is allowed about five minutes to explain why some things are transparent to visible light:
The basic idea is that when a photon is absorbed by a substance, an electron in the substance jumps from one energy level to another, corresponding to the amount of energy of the photon.
But it turns out that electrons can only exist in certain energy levels. (That discovery was what launched the entire branch of physics called quantum mechanics.)
And in the meantime, the energy of a photon depends on the wavelength or frequency of the light in question. If you imagine watching waves go by at a given speed, it's obvious that the shorter the distance between the wave crests, the more of them go by in a second. In fact, the wavelength times the number of waves per second (the frequency) equals the speed at which the waves go past.
It seems reasonable to suppose that the more waves per second, the more energy they carry, and that's true. Another way of saying it is that the shorter the wavelength, the higher the frequency, and the higher the energy level.
So since an electron can only exist in certain energy levels, it absorbs a photon only if that photon has the right amount of energy to take it up to the next energy level it can occupy. Otherwise the photon just keeps sailing on past, ignored. In transparent glass the possible electron energy levels are so far apart that photons can't be absorbed. In metals, on the other hand, electrons can occupy a lot of energy states, entire "conduction bands," so they absorb pretty much any photon that tries to get through. Other substances are in between. A brick for example, will typically absorb photons of visible light (unless it's a glass brick) but allow radio waves to pass right through. Radio waves are light, just with a very long wavelength and very low-energy photons.
Incidentally, this video is from the University of Nottingham, which I assume is where Robin Hood did his undergraduate work.