Doing it without permission: Worst case you pay for a new car.
Getting permission : Ask!!! .
Find a person who has the authority to approve your request and explain what you are trying to do and why.
It actually worked for us.
It's important to find somebody who is able to authorise your request.
Dealing with someone who is sympathetic but lacks authority will get you nowhere.
Real life example below.
We rented a car in Australia a few years ago - ALL rental companies had similar "no off road" clauses in their contracts.
They were generally specific enough that you could probably drive an Australian "outback" road but not take "unformed road" trails down to picnic areas, dams, lookouts etc.
We had our two adult children with us - we wanted to introduce them to a small glimpse of the "real" outback.
We decided to visit and stay at the world famous in Australia "Glengarry Hilton"
(yeah, right!!!)
- down about 50 km of roads that you wouldn't usually call roads near Lightning Ridge.
Some of the agreements said "without written approval".
The endeavour seemed doomed.
Non of the counter staff we spoke to had any expectation that such approval could actually be gained.
Nor did their supervisors.
Having identified the company that had the car we most wanted I did an internet hunt for company upper management and found a phone number of a State manager.
Instant success.
Full understanding of what we wanted to do.
Good explanation of WHY they had the policy - and a note that roads to picnic sites etc were fine - all they wanted was a road that had a formal description so the breakdown wagon knew where to find you :-).
He had only one question - "
How did you get my number " :-).
Full album here - to stay in roll mode, scroll don't click Glengarry Hilton - Wikimapia - zoom out until you see where you are :-} .
Yes.
No problem with driving there.
Don't be misled by the "green" surroundings :-).
travel.stackexchange.com/users/3301/Russell McMahon
What do I risk if I ignore the clause and drive on such trails?
Long story short you risk voiding any coverage you have on the vehicle, which will make you responsible for any and all damages that may happen.
Also most modern SUVs are not designed to be take off road and some don't even offer 4x4 capabilities, so it is very possible that you may not even be able to get to where you're going.
So how do you get there?
There are 4x4 and ATV tours like this one for Grand Canyon.
So if there is anything worth seeing your will have tours and if not you're likely to have places to rent similar vehicles.
travel.stackexchange.com/users/1372/Karlson
How can you visit those areas?
Simply take the right turn.
There are quite a few unpaved roads which are clearly marked - just look for them.
I've personally been on a few unpaved roads in Death Valley, Capitol Reef National Park and Monument Valley.
Use common sense: Sometimes the roads are quite easily accessible, even if they're unpaved.
Drive slowly, watch for potholes and if you don't feel comfortable: Turn back!
However: If your contract says that you're not allowed to drive on these kinds of roads and you get stuck or have any other kind of accident
I suppose it'll get quite costly.
But as they say: No risk, no fun! :)
travel.stackexchange.com/users/4742/perdian
We've had this problem for a number of years as we have relatives that live along gravel roads in various parts of Alberta.
Having looked at all the local rental companies there are basically two variations of the rental contract depending on the company.
The majority of the companies stipulate that the vehicle can only be driven on paved roads, which means we would be in violation of the rental agreements whenever we visited any of the relatives who live along gravel roads.
The others stipulate that the vehicle can only be driven on regularly maintained roads, which in the case of Alberta includes the gravel roads.
Talking to the various rental companies one said to us that if they restricted the rentals to paved roads only entire towns would be inaccessible by rental car.
Update:
Since I wrote my original answer for this we have now found one local Alberta rental company who explicitly allow some of their vehicles to be driven on the gravel roads rather than allowing it via a loophole, but only those in the SUV classes.
We came across them quite by chance because they are now the Fox Car Rental franchisee at Edmonton Airport
and I talked to them directly to confirm.
My basic advice though remains the same, the major rental companies will generally restrict usage to paved roads, but the key thing is to talk to the local rental offices as they may well operate different policies based on where you are going.
travel.stackexchange.com/users/33204/RTPeat
Fined 300 EUR for driving on Non Asphalt Roads.
In May 2014, we rented a car via Raddisson Hotels from Fastrent, Tallinn, Estonia.
As we were about to drive off the lot, the attendent said be sure not to drive off asphalt roads.
We did drive on one well maintained national park sand road.
Fastrent charged us 300 EUR for driving off asphalt road.
A well hidden line in Conditon 6 of 33 on the back of the contract says "Lesse can drive the car only on the asphalt roads."
travel.stackexchange.com/users/16402/TSmith
In the southwestern United States, many interesting spots are only reachable via off road trails.  Rental car contracts seem always to include a clause that disallows driving on such roads (even when renting an SUV).  How can I visit those areas?  What do I risk if I ignore the clause and drive on such trails?
How can I visit areas with unpaved roads in a rental car?
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<usa><driving><car-rentals>
travel.stackexchange.com/questions/14827
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If you do it without permission, you risk voiding your warranty and in the worst case, having to pay for a new car. Most modern SUVs are not designed for off road and may not even have 4x4 capabilities, so you may not be able to reach your destination. The key thing is to talk to the local rental offices as they may well operate different policies based on where you are going. Major rental companies do not allow off-road driving and it is considered a good ideea to get permission before doing it. Failure to do so means the driver is liable for all damages. It should be noted that most modern SUVs are not designed for off-road driving.
If you want to drive on non-asphalt roads in a rental car, get permission first or you may end up paying for damages. Most rental companies do not allow driving on roads other than asphalt. If you drive on non-asphalt road the insurance will be void and you will be liable for all costs. Modern SUVs are mostly not designed for off-road driving.