Chris Coleman's charges are currently preparing for the 24-team tournament in the Vale do Lobo training complex in Portugal, which has been previously used by England and Premier League club Manchester United.
"I don't know who planned it but it was unbelievable," Williams told British media of the base.
"It was good before but from the meetings we have had, there will be no excuses now. We can't say 'oh we didn't have this or we didn't have that'. Everything was taken care of.
"It means you can perform a little bit better... Now we can just concentrate on playing football -- and that is the way you want it."
By scoring seven and setting up two of their 11 goals in the qualifiers, double Champions League winner Gareth Bale has been integral for Wales and Williams said the Real Madrid winger's experience on the big stage would be pivotal.
"He is a player who has always been there when we have needed him. We are going to need him through this tournament definitely, it is on the world stage and everyone will be watching," Williams said.
"His experience will be valuable in and around the dressing room. He has the most experience of all of us of big occasions, and he normally he doesn't let us down."
Midfielder Joe Ledley is the only doubt in the provisional squad after he fractured his leg earlier this month. Coleman will cut six players from that list and name his final 23-man squad for the June 10-July 10 tournament on Tuesday.
(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by John O'Brien)
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