Closed tabs can usually be recovered in two ways...
1) If the tab is manually closed, it can in many cases be recovered/reopened. With the Safari browser opened, touch-and-hold the “+” icon (top-right of the page); this will open a list of recently closed tabs. Simply select the tab you wish to reopen - and viola! Note also that the tab history is also recovered. It should be noted that tab recovery generally only works for tabs closed within the current session.
2) If a tab is not directly recoverable, you can identify websites recently viewed from the History list. Simply touch the book-icon (top-left of the page) - then touch the History (clock) icon to reveal the recently viewed sites in reverse chronological order. Tap the page you wish to reopen.
Hope you find these tips helpful.