She is still a commissioned ship of the Royal Navy. Yes, you can visit and either go round listening to an audio guide or book a guided tour. I’d recommend taking a guided tour. You would be shown around by navy personnel and learn more. There is a lot to see just on that ship. I’d suggest going in low-season. It’s very busy in the Summer. She is after all the most famous ship in the U.K. and the place of death of her most famous sailor, Admiral Lord Nelson.
At the Battle of Trafalgar in 1805 the combined French and Spanish fleet was defeated and Napoleon's plans to invade England were ended. So started the demise of the Napoleon the evil despot. He was finally defeated at The Battle of Waterloo in 1815 by the Duke of Wellington. Admiral Lord Nelson was shot by a French sharpshooter (sniper) from the Redoutable and fatally injured. Nelson had insisted on remaining on the deck of HMS Victory even though his men had cautioned against it.
@jtk It's very cramped onboard. Warships were not built with comfort in mind especially in 1759! A lot of the time I had to stoop because the ceilings are so low. It's also rather dark and quite crowded with people. Not the best photo opportunities onboard unless you could time it to a very quiet time.