You could simply try searching for the address on a search engine that indexes .onions which should give you an idea of what the site is about.
If that doesn't work:
Since your concern seems to be about downloading illegal images, you might want to simply block images from loading while visiting that site. This can be done in Firefox's
about:config by setting the value of
2 (it doesn't seem to block all images, for example "icons" and some other content still loads).
This will make your browser stand out among other users who visited the site, but as long as you reset the setting to default for anything else you do on Tor, this shouldn't harm your anonymity.
You probably want to block video and sound as well. If you're concerned about some content still loading, find a way to actually make Firefox only load text.
Simply connecting to a site and/or downloading some text from it shouldn't be illegal (I am not a lawyer and I do not know your country), but you might want to check your jurisdiction.