I know it may look strange for you, I think there are very few countries where elections are obligatory.
Let me explain a bit off topic here: "they" send us an "invitation" to go and vote, we have to go to the voting station that is on that paper (not to anyone!), that is mostly in a school in the neighbourhood.
You can give a procuration to somebody to vote in your place, BUT........... I have no wife, my parents live 35-40 kms from my house (and they cannot do my voting in their place) and I don't want to bother the neighbours with it.
As coincidence happens, most or our elections have always been on the Gaydon date (or before when it was in Rugby).
In the early years (I go to Gaydon since over 20 years) I had to go on Sunday morning to a local police station where they had to write me a paper declaring that I was there on thàt Sunday morning. Well, I can tell you: explaining what I needed was not the easiest part in a country where voting is voluntary!!
Later the rules became less strict and my crossing ticket (ferry or tunnel) was ok as proof I was away.
If you don't vote and you cannot prove you were away (or in hospital or something), it can cost you at least 50 euro, money which I can spend better in a modelshop ;D ;D