1) stone 2) books if printed on the right kind of paper 3) metal if it's not something subject to rust
Even if it is possible to make a website that lasts 500 years, I expect we haven't figured out how yet. I'm sure it took people a while to figure out how to make long-lasting tombstones; early North American ones were often made out of sandstone or wood, and are illegible or completely gone now. You may be one of the very first people to give thought to how to make a website that will last that long; what are the odds you will get it right on the very first attempt?