Tourists and other visitors (not including Royals!) 
Attempts to have royal visitors travel through Fern Gully in the 1920s seemed doomed to failure!
In 1920 the very popular Edward, Prince of Wales, was supposed to include Jamaica as a stop on a wider tour he was making: naturally plans were made! 

      Daily Gleaner, August 5, 1920

but then something went wrong -

Daily Gleaner, August 21, 1920

(By the Man on the Street).

Thousands of persons throughout the island are disappointed at the fact that His Royal Highness the Prince of Wales will not visit Jamaica month. The Prince's visit has been

postponed owing to the alarming number of cases of chicken pox in the Island. The disease has now assumed epidemic form and it is irony that the Central Board of Health who turned down the repeated recommendations of the City Council and the St. Andrew

Parochial Board to make chicken pox a notifiable disease should be the very body to recommend that the Prince should not come to Jamaica!

Things didn't go much better in 1927 when the Duke and Duchess of York visited. (Later to be King George VI and Queen Elizabeth) 

Daily Gleaner February 3, 1927

Disappointed St, Ann

It was a real disappointment to the St Ann people that

the weather prevented the Duke and Duchess from

taking the trip through the Fern Gully to Ocho Rios. This

is one of the best bits of scenery in Jamaica, and of its

kind quite unique. Even in a pouring rain it would be wonderful, and I think it was a mistake to change the

route. The difference in distance was only a matter of

about ten miles; and if their Roya1 Highnesses had to

drive through rain, it didn't much matter what road they

went by. Considering that preparations had been made

to greet them, and that numbers of persons were gathered at different points of the route, I think it was a

pity to disappoint them. We can't always have "Queen's weather," and it should not have been forgotten that

our visitors are more accustomed to rain than sunshine.

They had fine weather for the first part of their trip from

Kingston to Moneague via Bog Walk and Mt. Diablo,

which enabled them to see to advantage some of the best scenery that Jamaica has to offer.

I hope one of the Royals eventually got to see the famous Fern Gully; I must keep my eyes skinned! (ah - 1953 - Queen Elizabeth, newly crowned, and Prince Phillip, actually made it)
There were, of course, visitors who made it through Fern Gully and some of them recorded their comments.

Stephen McKenna in an article in the Times of London,  April 28, 1923 -

'The two-mile tunnel of Fern Gully is pure


 Daily Gleaner, May 22, 1926
  Daily Gleaner, November 14, 1929
 . . . and oh yes, the Moneague Hotel was still up and running some 4 decades after the great Exhibition of 1891 which had brought it into existence!
 The Moneague Hotel is not far from Dunn's River, a famous bathing beach where fresh water falls tumble into the sea. Roaring
Falls, and the beautiful Fern Gully
also near Moneague.

J. POWTER, Director, Jamaica

Government Railway,

in Baldwin Locomotive Quarterly. (1928)