Can I get a pointer to a Span?

Try this:

Span<byte> bytes = ...;
string s = Encoding.UTF8.GetString((byte*)Unsafe.AsPointer(ref bytes.GetPinnableReference()),
    bytes.Length);

If you have C# 7.3 or later, you can use the extension made to the fixed statement that can use any appropriate GetPinnableReference method on a type (which Span and ReadOnlySpan have):

fixed (byte* bp = bytes) {
    ...
}

As we're dealing with pointers this requires an unsafe context, of course.

C# 7.0 through 7.2 don't have this, but allow the following:

fixed (byte* bp = &bytes.GetPinnableReference()) {
    ...
}