All right then. I would suggest driving on HWY 1 up the Fraser valley to Chilliwack. There are a ton of old FSR's up in there, as well as two gorgeous lakes, if you don't mind a side trip. Then if you go on to Hope, you can visit the Othello Tunnels, which is an absolutely spectacular hike through some old train tunnels. Then I would recommend traveling up the famous Fraser Canyon - it's centuries of history piled on top of itself. You could visit a lot of the spots I did on my day trip like The Lady Franklin, Old Alexandra Bridge, The Alexandra Lodge and graveyard, the old sections of highway and the old Hell's Gate tunnel, Spuzzum, North Bend, etc. Some really spectacular scenery up there. If you keep to the right highway fork at Spences Bridge and look out for the first dirt road on your left after you cross the river, there's a track that goes way further up the canyon and leads to an old ghost town with an abandoned church called St. Aidan of Pokhaist. It's really cool. I tried to go there on our last trip but we got diverted by a flat. The road looks like it doesn't go anywhere on google, but it does clearly, if you check the satelite. Unfortunately I can't tell you whether there are gates or anything. I've seen pics of people at the church in their 4x4s, so it's probably open.
There's also the most iconic of all BC 4x4 tracks, the famous Whipsaw Trail. That's off of Hwy 3, the Hope Princeton, so that's the other direction from Hwy 1 and the Fraser Canyon. Perhaps do a loop and hit it on the way back, or on the way in. Whipsaw is rated as a moderate trail that takes about 2-3 days to complete. It has some abandoned buildings and a lot of history, as well as a gorgeous camp spot about midway at a lake. That one is on my bucket list for sure.
If you have time for a lengthy detour, the incredible modern ghost town of Kitsault is not super far from the road to prince rupert. I believe it's about 3h on a dirt road out of Terrace. It's a mining town that was abruptly shut down in 1982 when the price of molybdenum (the ore they were mining nearby) bottomed out and the US company that owned it shut the town and kicked everyone out. The thing was, they left the power on, and the town ended up being bought in 2005 by a millionare who wanted to make it into first a retreat for intellectuals, and then an LNG hub, but none of that panned out. Word on the street is that if you ask the caretakers nicely and they don't think you're hooligans, they'll give you a tour. The ghost town of Alice Arm is right across the bay from Kitsault.
If you have time, you may also want to pay a visit to Haida Gwaii, formerly known as the Queen Charlotte Islands. It's about a 5 hour ferry ride out of Prince Rupert, I believe.
If I think of any other spots, I'll post more. Good luck to you! :)