There are a fair few places on the World Heritage list that present particular difficulties to visit, mostly due to their location but there are a few with other reasons stopping a visit.

But are there some sites that just cannot be visited by tourists?

Altamira Cave (Esp) – the cave is closed to all visitors to prevent the deterioration of the paintings. There is a replica open though.
Thracian Tomb of Kazanlak (Bul) – same as Altamira
Lascaux cave (Fr) - is also closed but there are other sites inscribed as part of the Vezere Valley that are accessible
Gough Island (UK) – only a handful of lighthouse keepers and scientists are allowed to land on this already pretty remote island. Not sure if it is possible to land on Inaccessible Island though
Heard and McDonald Islands (Aus) – I am not sure about these, whether they are just tough to get to or if they are only accessible to scientists
New Zealand Sub Antarctic Islands (NZ) – same as above, though I think there are some tour companies that offer trips that actually land here.

Soon to come?
Surtsey (Ice) – perhaps to be added to the list in 2008 only accessible to scientists studying it.
Palace Stoclet (Bel) – You can see the outside but the interior where the real outstanding Universal value lies is out of bounds. Doubt it will get onto the list though mostly due to the private ownership and the threat of all its valuables being sold of by the current owners.

I personally think I would count many of these as visited had I seen the replica sites or done a lap but for the really picky ones amongst us can these ever be 'ticked off'? Are there any more?

Mt. Athos is forbidden to visit for women!

Yes I had thought of 2 ideas for Forums in this area
a. Sites which discriminate in their entry requirments - Mt Athos is 1 but most of the others are going to be Mosques re non muslims and do we want to go down that road .......?

b. How to visit the really difficult ones. I know that Els has mentioned to me in the past that, if you throw enough time and money at the problem, then EVERY site can probably be visited - leaving aside issues of only being able to see the outside etc (In Natural sites the equivalent is not being allowed into the inner reserve unless you are a scientist). Could I see if this was true? In fact all of the first sites I looked at I WAS able to work out how to get to them (whether it would be worth the time and money is another matter!) I have actually visited both Gough Island AND Inaccessible - and can tell you how to do so if you wish (see my review of Gough). As you say Gough can't actually be landed upon unless you work for the SA weatherbureau and stay a whole year! But the site can be visited by Zodiac as the coast line is included (and you can "touch" a stac!). Inaccessible can be landed upon if you have soemone from Tristan with you - and the same trip as does Gough does arrange that (weather permitting) each year.
Wrangel Island is available on a tour as are Heard/Mcdonald AND the NZ sub-Antarctic Islands. The "Spirit of Enderby" is the boat for these places (see Google). Henderson HAS been available but isn't necessarily on a published Pacific itinerary EVERY year. Of course you could have your own yacht.....! The first time I ran into a problem were with those sites in war zones or failing states such as in DRC (and currently Iraq) - I suspect that most of the REALLY hard sites to visit are in Africa - particularly DRC and CAR. I am currently planning a trip to Cameroon and could get to Dja but have decided that it really isn't worth the time and cost. I had my problems with Omo Valley in Ethiopia too and had to stretch the definiton of "see" a bit !!
On her site Els says of Jebel Barkal/Sudan "This is undoubtedly one of the most difficult places on this list to go to". I think this is left over from the early days of her Web site and that she is older and wiser now - there are several tour companies which will get you there!

I'm now so old that I didn't even remember that it was there (the sentence about Sudan) ......

Ah good point about Mt Athos, I knew that one as well just forgot to include it.

Seeing the interiors of places in Europe is normally the only time they become tricky, but very few are you acctually unable to see. Though the thorn in my side is in this category it is the interiors of the Works of Victor Horta in Brussels, especially Hotel Tassel. On my last four trips to Brussles I have chosen to have my lunch/ coffee on the pavment outside in the hope that the owner will come by, take pity on me and let me view the staircase, needless to say this has never happened. It seems to be the only one of the houses that never seems to open its interior.

Does disability access – or lack of! – fall under the question: Which sites are impossible to visit? If a site does not have wheelchair access then it does not have baby pram access which really limits the purpose of cultural education for the masses. Any comments?

"Palace Stoclet (Bel) – You can see the outside but the interior where the real outstanding Universal value lies is out of bounds. Doubt it will get onto the list though mostly due to the private ownership and the threat of all its valuables being sold of by the current owners."

actually, if I recall correctly, a ministerial decree was issued a bit back, stipulating that the valuables inside Palais Stoclet/Stocletpaleis should remain in situ. The owners can still use them, but they are not allowed to sell them or let those valuables leave the palais.

Ah that is great news if that is the case. I 'visited' a few years back and the court case was still being drawn out.

Great news if it has been protected. There was a rummour that one of the siblings wanted to retain all the interior and open it up to the public, but the others were not happy with the idea.
Maybe it can be opened up!

I decided to look around on the net, cause I was starting to doubt a bit, and I found an article which indeed says that the interior is protected (the article says fourniture, but I assume they mean everthing inside). Warning though, it's in Dutch.

There was indeed a court case, Brussels capital region wanted to protect the fourniture and the family went to court, but court disagreed with them. I assume the brussel capital region protected the interior in preparation for world heritage inscription.

If you're ever able to go inside, I don't know. The house is still privatly owned, and I got the feeling they don't like all this attention. Perhaps one day when they sell it...or move out...

I was also thinking about the belgian house of Le Corbusier on the tentative list. It's also privatly owned (even by a belgian celebrity if I'm not mistaken) and can only be visited from the outside.

I think we should keep that separate from this issue as unfortunately I would imagine there would be a huge amount of sites that are not accessible to many disabled visitors.
Whilst some sites may have visitor's centres that are more accessible, many sites themselves could be nigh on impossible for wheelchair users to access. e.g. Skellig Michael (Ireland)

I remember watching a programme about wheel chair users accessing different WHS in Britain. The Tower of London and Westminster faired reasonably well. The centre of Edinburgh came in for some criticism because of the cobbles and hills. These are integral aspects of the site that hinder access, even if the site does try to promote accessibility.


I must admit it is not something I have really noticed but are there any places that are notable for the way they encourage access? Also are there any other places that really work hard to make visiting more relaxing/ enjoyable even for able bodied visitors?

Kazanlak

The real tomb can be visited. There is another fee for it, though. It was 20 lv in 2005. One has to insist to be shown the real tomb. atip is to call the director of the History Musuem, Kazanlak and he will come and open the tomb.

The Heard Island Web Site states under FAQ "Can I visit"
"Technically, yes, you can visit Heard Island if you apply to the Australian Antarctic Division for a permit to enter and undertake activities in the Territory of Heard Island and McDonald Islands (HIMI). The catch is that Heard Island is a long way from anywhere (approximately 2 weeks sail from Australia) and you have to pass through some of the roughest seas on the planet to get there, and back home again. Such voyages are very costly require considerable planning and logistical support.
For those reasons, there are currently no commercial tour operations that visit Heard Island"

Well, if you REALLY want to tick it off and have between US $16000 and $20000 spare as well as a month free this November/December, here is how you could go! 10 days sail each way and 3 days there (with a "pass-by" of McDonald)!
http://heritage-expeditions.com/trip/south-indian-ocean/

PS
With reference to the recent Forum discussion on the Connection related to - Formally Inhabited, Never Inhabited and Uninhabited - Heard Island should be added to "Formerly Inhabited"
"In the sealing period from 1855 to 1880, a number of American sealers spent a year or more on the island, living in appalling conditions in dark smelly huts, also at Oil Barrel Point. At its peak the community consisted of 200 people. " (Wiki)

Pff.
Sailing for 10 days: "You can see Albatross!!"
3 days ticking of WHS
Sailing back for 10 days, looking for more sea birds