Hi!
I used one as the DM in 1E in the mid 80's. The confrontation was the end game in the arduous task of collecting the pieces of the Rod of Seven Parts.
The last part was in the belly of the Tarrasque itself!
The group was known as the Thunderlords, due to one of its members wielding the hammer of thunderbolts!
The party consisted of:
Eruze Solnor 14th level Human Fighter
"Archer" (real name was a secret, went by this pseudonym), 9 Level Cleric/8 level Fighter/ 8 level Magic User, Half-elf
Erik Stoneheart 12 level thief/ 9 level fighter Dwarf (wielder of the hammer of thunderbolts).
Houdin Spellbinder 12th level Magic User
Cantum, the voice of Pelor 16th level Cleric
To even prep for such an encounter was in itself a mini-campaign, since they needed to quest for the wish spell to end it as well as other potent magical artifacts to survive the ordeal.
The battle was brutal, I didn't pull any punches. Archer was swallowed alive and died within, although he wasn't digested....
Erik Stoneheart lost his right arm and died of the shock....
Houdin cast all the spells he knew and ultimately had to become invisible and hide, lest he be eaten... Although he does bear the ring with one wish in it....
Cantum, voice of Pelor, lost his mighty mithral armor and holy magical shield, ripped to shreds by the beast, hanging on for dear life.
In the end the mighty Eruze Solnor went toe to toe, his platemail of etheralness keeping him alive, his prodigious amount of hit points being worn down finally lands the final blow to knock the beast unconscious.
The invisible wizard casts the one wish from the ring to slay it forever! From its belly they recover the last shard of the rod, precious gems and enough hide to later forge one +5 shield to replace the priests lost one!
Probably their grandest battle....
..except for that battle with Lolth's giant adamantium spider, but that's another story....
Primarchone