I always thought that whenever someone buys a car sound system, it should allow connecting of mp3 players as input device. The car I got doesn’t have that type of sound system and I didn’t want to buy a new system for that.
Yesterday, I found out that there exists a car cassette adapter that allows you to connect your mp3 player to a sound system which only supports audio cassettes or audio CDs with no external input source. Rare in modern world but most builtin systems are like that in smaller cars in Pakistan.
In Karachi, Pakistan, it can be bought for 250 PKR (2.5 Euros). The cassette has an audio cable to connect to your favorite mp3 player and of course has no tape in it. Its head does the magic of playing music by faking as a real cassette with rolling magnetic tape over it.
Here are pictures of the adapter I bought.