Inherited Mid-Early 20th Century European Stamps

I just found a box with my grandfather's stamp collection and need some advice on where I could sell/donate them and how much they would be worth.

There are around 500 stamps from many European countries dated from 1920-1950. I know almost nothing about stamps so thought I'd reach out on this forum. My contact number is *** Private information removed by Staff. Please do not post your address/email/phone number etc. *** in case anyone is interested or has advice. :)

Thank you,
Walter

Walter - hello. Please post some pictures. And best to avoid personal contact details!

Walter,
Welcome to the forum.
Without seeing the content, if it's around 500 stamps from 1920-1950, the probability of much value is low. However, that could depend on a number of things. If these are "on cover" (still on the envelope, or post card), then their is a chance for higher value (particularly if they are correspondence during the First or Second World Wars).
Can you tell us more about what they are? Are they just used stamps loose in a box?