Barendd Nobeard
Explorer
Yup--the Tarrasque has a +38 Fort save in the SRD.
I'm sure there are better builds out there, but off the top of my head you can get it to +30 very easily. But getting to +40 is pretty hard.
Grey Elf, start with INT = 20.
Put all stats bumps in INT, 20th level character = 25
Tome of Clear Thought = 30
Headband of Intellect = 36
Spellcasting Prodigy = effectively 38
INT 38 = +14 mod
Fifth level spell: DC = 10 + 5 + 14 = 28
Spell Focus: appropriate school = +1
Greater Spell Focus = another +1
Total so far = 30
What else can pump up the DC?
I'm sure there are better builds out there, but off the top of my head you can get it to +30 very easily. But getting to +40 is pretty hard.
Grey Elf, start with INT = 20.
Put all stats bumps in INT, 20th level character = 25
Tome of Clear Thought = 30
Headband of Intellect = 36
Spellcasting Prodigy = effectively 38
INT 38 = +14 mod
Fifth level spell: DC = 10 + 5 + 14 = 28
Spell Focus: appropriate school = +1
Greater Spell Focus = another +1
Total so far = 30
What else can pump up the DC?