The best advice I had in 1995 when I inherited about £100k was to do nothing until I was comfortable with having that amount of money.
Then I was advised to pay off all debts, of which I had none, increase pension contributions to maximum, to minimise tax liabilies, and then consider what to do.
Things are rather different now in respect of financial advice, I would suggest you really need to take professional advice. As how you "invest" your money will depend on your age, your aspirations, your attitude to risk and even what other assets you have and what you wish to leave to your dependants. Are you looking for growth or income?
Although cash ISAs are safe, the returns are pathetic.
I am not a financial adviser, but did quite well with my invesrments just by reading the Telegraph financial pages,