For her birthday, you should take your wife somewhere that suits her interests and personality, and that will create a relaxing and romantic atmosphere for the two of you. This could be anything from returning to the place where you had your first date to going on an exotic vacation.
Depending on the type of activities your wife enjoys, you have many options. She may enjoy a party at home with close friends or a romantic dinner for two at a restaurant she has been wanting to try. If you are planning a trip for her birthday celebration, it need not be expensive. She may prefer a trip to a romantic nearby spot, such as a bed and breakfast or winery. Doing something thoughtful and personal is always the best gift.