Yes, you can enter without guidance and welcome to do so. It seems a bit scary if you never enter the Sikh temple, but I did it myself and these people are very friendly and hospitable. Leave your shoes on your toes and wear a scarf to cover your head. You can also enjoy delicious vegetarian dishes for free, but donate to the temple. You can also visit the chapel. It may not be as ornately decorated as some Buddhist temples, nor does it appeal to an impressive look, but it is a unique experience that you must embrace to learn more about religions that many people are not familiar with.