Is it permissible to benefit from holiday vouchers, of which the employee pays only 30% of their value, and which are used at travel agencies, restaurants, museums, and the like?

If the vouchers enable you to purchase specific items for a certain amount, then there is no objection to accepting them, as they are a gift from the company. However, if the vouchers allow their purchaser to obtain discounts that may or may not materialize in exchange for money, then this is prohibited gharar (uncertainty/risk). The Islamic Fiqh Council of the Muslim World League and the Permanent Committee for Issuing Fatwas have issued rulings prohibiting dealing with paid discount cards due to the gharar involved.