I have an idea for a website whereby people use Bitcoin to buy access to a multi-user game and compete with each other in a variety of games such as puzzles, mystery games, etc. Funds from usage fees would go into a wallet and whoever solves the game first wins the entire contents of the wallet.
Are there any legal restrictions, in any country, for this type of activity?
Thanks
You'll technically need to get a license, gaming or not, for the majority of countries in which gambling is regulated imo.
The fact is that most countries around the globe don't really care if you simply offer games - but will get on your tail immediately if it's got anything remotely to do with real world currency, due to the strict AML/KYC standards imposed globally now, which BTC is now under, unfortunately.
Your idea isn't technically a casino per se, but does have elements of chance, as well as potential points that can be exploited by players and the people behind the site in the regulator's eyes. You will probably find it possible to run such a site unregulated in certain countries, though, especially if it's a small scale operation.